Building Construction: Principles & Practices Textbook

M SERIES Macmillan Texts for Industrial Vocational and Technical Education I If 'V %*. X ■IS I If BUILDING CONSTRUCTION PRINCIPLES AND PRACTICES D. Walton i £32 0 Barnfield College Library CO fu-b2 Building Construction 3ARNFIELD TECHNOLOGY CENTRE LIBRARY ENTERPRISE WAY LUTON LU3 4BU TEL: 01582 569547 This book is due for return on or before the last date shown below. FOR REFERENCE ONLY Don Gresswell Ltd., London, N.21 Cat. No. 1207 DG 02242/71 Digitized by the Internet Archive in 2020 with funding from Kahle/Austin Foundation https://archive.org/details/buildingconstrucOOOOwalt THE - SERIES - Macmillan Texts for Industrial Vocational and Technical Education Building Construction: Principles and Practices Denis Walton & MACMILLAN Macmillan Education Between Towns Road, Oxford 0X4 3PP A division of Macmillan Publishers Limited Companies and representatives throughout the world www.macmillan-africa.com ISBN 978-0-333-60522-6 Text © Denis Walton 1995 Design and illustration © Macmillan Publishers Limited 1995 First published 1995 All rights reserved; no part of this publication may be reproduced, stored in a retrieval system, transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the Publishers. Illustrated by 1-11 Line Art Photographs courtesy of Househam Henderson Moteane, Architects Cover illustrations courtesy of Images Colour Library Printed and bound in Malaysia 2008 14 13 ontent Introduction 1 2 3 4 5 viii Health and safety 1 Introduction Working safely Check your understanding Revision exercises and questions 1 1 4 4 The building team 5 Introduction The client The design team The construction team Working together Check your understanding Revision exercises and questions 5 5 5 6 7 8 8 The site investigations 9 Introduction Considering the suitability of a site Surveying the site Drawing up the site survey Check your understanding Revision exercises and questions 9 9 10 10 12 12 The construction documents 13 Introduction The working drawings The specification The bill of quantities Check your understanding Revision exercises and questions 13 13 14 16 17 17 Preparing the site 18 Introduction Setting up the site Clearing the site 18 18 21 Revision exercises and questions 21 21 Setting out the building 23 Introduction Setting out the building outline Fixing the corners in place Setting up a site datum for vertical levels Check your understanding Revision exercises and questions 23 23 25 27 29 29 Excavations 30 Introduction Removing the topsoil Digging a trench for strip foundations Supporting the sides of an excavation Excavation plant Working safely in excavations Check your understanding 30 Check your understanding 6 7 8 9 Revision exercises and questions 31 31 34 37 37 38 38 Foundations 39 Introduction Foundation loads Types of foundation Designing strip foundations Designing pad foundations Check your understanding Revision exercises and questions 39 39 41 46 47 47 47 Walls 48 Introduction Types of wall Characteristics of walls Building materials for external walls Technical words used in bricklaying Bonding 48 48 49 49 52 53 V Contents Openings in brick walls Lintels Arches Technical words for parts of arches Cavity walls Stone walls Block walls Non-load-bearing external walls Non-load-bearing internal walls Check your understanding Revision exercises and questions 10 58 59 61 62 65 65 68 70 70 Sf Fireplaces and flues 76 Introduction Technical words for parts of fireplaces and flues The dimensions of brick fireplaces and flues Building a fireplace and flue Check your understanding Revision exercises and questions 76 11 Floors Introduction The oversite concrete slab Concrete ground-floor slabs Laying an oversite concrete slab The raft foundation slab Curing the concrete Building a suspended timber floor Timber flooring Upper floor construction Reinforced concrete first-floor construction Making a hollow pot reinforced concrete floor Check your understanding Revision exercises and questions 12 Roofs Introduction Technical words for parts of a roof Pitched roofs The structure of a timber pitched roof Connecting the trusses Using tiles as roof coverings Using roof sheets as roof coverings Flat roofs Building a reinforced concrete roof Waterproof roof finishes Insulating a flat roof Wind effects on flat roofs Check your understanding Revision exercises and questions 76 77 78 79 79 80 80 81 81 83 83 84 84 85 85 88 90 91 91 92 92 93 95 95 98 101 105 106 107 109 113 113 113 114 Scaffolding 115 Introduction Technical words for parts of a scaffold Types of scaffolding Regulations and recommendations for scaffolding Check your understanding Revision exercises and questions 115 115 116 116 118 118 Stairs 119 Introduction Technical words for parts of staircases Staircase materials Staircase layout Assembling a timber staircase Making a concrete staircase Check your understanding Revision exercises and questions 119 119 119 121 122 124 127 128 15 129 Introduction Technical words for parts of a door Door construction Flush doors Panelled doors Ironmongery Door dimensions Door frames and linings Check your understanding Revision exercises and questions 16 Windows Introduction Technical words for parts of a window and frame Building regulations for windows Types of window Window height Glazing Excluding water from timber windows Using metal windows Making window cills Fixing windows to openings Keeping out intruders and insects Check your understanding Revision exercises and questions 17 Drainage Introduction Technical words for parts of a drainage system 129 129 130 133 133 135 135 137 137 137 138 138 139 139 139 139 141 143 143 143 144 145 145 146 147 147 147 Contents Principles of soil drainage Types of drainpipe Excavating the drain layout Testing drains Building a manhole Septic tanks Discharging the effluent Check your understanding Above-ground drainage A single-stack plumbing system The sanitary fittings Check your understanding Rainwater disposal Check your understanding 147 149 150 151 153 153 156 157 157 l6l l6l l6l 162 166 Revision exercises and questions 166 18 Water supply Introduction The cold water supply Hot water installations Pipes and fittings Check your understanding Revision exercises and questions 168 168 168 171 174 176 176 VII Check your understanding 196 Revision exercises and questions 196 21 Concrete technology Introduction Materials used to make concrete Concrete mixes Making concrete by volume Adjusting the water content of damp sand Grading coarse aggregates Testing concrete and its materials Reinforcement in concrete Concrete mixers Check your understanding 197 197 198 199 201 201 203 204 204 204 Revision exercises and questions 206 22 Soil technology Introduction Load-bearing capacity Check your understanding Revision exercises and questions 23 Timber technology 19 Electrical installations 177 Introduction Simple electrical theory Electrical wiring Check your understanding 177 177 179 181 182 Revision exercises and questions 197 Introduction Softwood and hardwood trees Making timber from trees Timber sizes Joining timber Check your understanding Revision exercises and questions 207 207 207 209 209 210 210 210 213 214 2l6 216 216 183 24 Structural loads Introduction Plastering External render Painting Floor finishes Finishes on concrete subfloors Wood finishes on concrete subfloors Laying tiles on concrete subfloors Finishes on timber floors Wall tiling 183 183 187 187 189 190 192 193 195 195 217 Introduction Compression loading Reactions and moments Check your understanding 217 217 220 221 Revision exercises and questions 221 Answers to revision exercises and questions Key words and definitions Index 222 229 233 The purpose of this book on Building Construc¬ tion: Principles and Practices is to help students who are studying this subject as part of their technical education. The content of the book matches a typical syllabus in a senior secondary school or college where technical and vocational studies are part of the curriculum. In this book you will find information about the materials used in construction and how to build the different parts of a small building such as a house. The focus of the book is always on the safe construction of a healthy and durable building. The aim is to give you practical information on techniques and the performance of building ma¬ terials. With further training, this information could lead to employment in the building industry. The emphasis is on practical applications, which use the equipment and materials commonly found on small building sites. This book, used with class¬ room and workshop instruction, as well as site visits, will give you a comprehensive outline of the procedures to build a house from the initial idea to choosing the finishes. VIII As a technical student you should understand the basic performance expected of a building. For example, a building must not collapse because of incorrect design or construction of the foundations. The materials used in a building must be durable and resistant to climatic extremes. A building must be well lit and ventilated. It should be cool in hot weather and warm in cold weather. If the building has bathrooms and toilets, then they should be hygienic. A building must be stable, durable, sanitary and fire-resistant. You can see a building with these features in Figure 0.1. These are the basic aspects of good building construction. In this book, you will learn how to apply the principles and practices to produce these re¬ sults in a safe and healthy working environ¬ ment on site. Introduction Figure 0.1 The elements of a sound building. IX * Heal Introduction A building site can be a dangerous environment. Powerful machinery, hazardous materials, scaffold¬ ing and trenches create risks for the building work¬ ers and other people in the construction area. This chapter describes some of the safe working prac¬ tices that can prevent accidents happening from carelessness or inexperience on building sites. Working safely Accidents will happen on building sites, but the number can be reduced by developing the skills that you need to do your work safely. By keeping your eyes open and thinking about the work on site, you may be able to work out in advance the safest methods for carrying out different jobs. This helps you to avoid methods that might endanger yourself and others. Remember - you will improve your safety record if you use the correct tools and equipment properly. Wearing protective clothing You should keep your working clothes in a safe place on site so that you can change in and out of them each day. A locker is useful so that you can store your personal effects securely while you are working. The best working clothes are overalls and strong boots. If you are working in wet weather you will also need rubber boots. You should al¬ ways wear a hard hat to protect your head in case anything is dropped from above or if you hit your head on a sharp edge on the site (Figure 1.1). Working in excavations A site may have many excavations or holes. If shallow excavations are not protected, then they should be surrounded by excavated material. Deep excavations must be surrounded by barriers. When you are working in a deep excavation you may not be seen by other people working at ground level. To work safely, you should always: 1. wear a hard hat to protect your head in case something is accidentally thrown or dropped into the hole; 2. put supports against the sides of the excavation so that the soil cannot fall in on you. Depending on the weather and the type of soil, excavations can be wet or dusty. If it is wet, then you will need rubber boots to protect your work shoes. In dry, dusty conditions you should wear a mask to cover your mouth and nose. Excavations should be inspected daily before anyone is allowed to work in them. This is very important after heavy rain. If excavations are blasted out of rock, then all the building workers should leave the site before the charge is fired. Only very experi¬ enced people should carry out blasting. Heavy loads and machinery should not be too close to the edge of any excavation. Too much weight can cause unsupported ground to collapse and the heavy load to fall into the hole. 1 2 Building construction to the equipment and lighting may get rough treat¬ ment. For this reason, it is extremely important to inspect and check the condition of the wiring at regular intervals. Ideally, the electricity to power tools and lights should be 110 volts and connected to transformers instead of 240 volt supplies. The reduced voltage means that an electric shock is less likely to be fatal. Figure 7.7 Protective clothing. Working with dangerous materials If a person suffers an electric shock on site, then follow these steps: Turn off the electric current. Make the person comfortable with as little movement as possible. Cover the person with extra clothing or a blanket for warmth. • Check the strength of the person’s pulse. • Use artificial respiration. Contact an ambulance. A building site may have many dangerous ma¬ terials such as: # explosives and detonators; • petrol; # cellulose thinners; • caustic cleaners; 6 paraffin. Careless use of these materials can cause consider¬ able harm to the building workers. Some simple precautions can prevent accidents or theft. Explosives and detonators must be cleared from a site when they are not in use. When they are kept on site, they must be locked in a safe place, and the site should have a record book which lists: 1. the amount of explosive received; 2. the amount of explosive used; 3. the amount that remains. The petrol that fuels the machinery must be kept in a locked compound. If a considerable amount of petrol is needed, then it should be stored in a brick enclosure. Diesel is a better choice than petrol because it does not catch fire so easily, but it should also be locked away. Cellulose thinners, caustic cleaners and paraffin should be stored in locked areas so that their use can be controlled. Working with electricity You can power machinery and temporary lighting with electricity. Because building sites are often wet places, electric shocks are possible. The wiring Working on scaffolding Working on scaffolding is one of the most danger¬ ous building activities. Building workers can acci¬ dentally fall off a platform, or parts of the scaffold¬ ing can drop and injure someone underneath. If building workers instinctively move around the platforms and ladders without looking down, then they could fall if the position of the scaffold¬ ing is changed. Workers on scaffolding must al¬ ways stay alert and check that they can place their feet and hands safely. Scaffolding, like the building it is attached to, carries staictural loads and stresses. To prevent accidents, experts must erect scaffolding to the highest safety standards. Its position should not be changed unless the proper supports, platforms and barriers are provided in the correct locations. The technical requirements for the safe erection of scaffolding are described in Chapter 13. Working with formwork Timber props and platforms support suspended floors made from reinforced concrete. This support framework is called the formwork. Erecting the formwork requires skill and experience be¬ cause the combined weighs of the wet concrete, the building workers and the machinery is consid¬ erable. Any weakness in the design or construc¬ tion of the formwork could have dangerous consequences. Health and safety Working with cement Cement is a safety risk for a number of reasons. It can: 1. burn bare hands while it is drying out; 2. cause skin diseases such as dermatitis; 3. be dangerous if it is inhaled as dust. You should wear gloves when you handle cement. If cement dust is present, then you should wear a breathing mask. ▲ You should be careful when you push wheelbarrows that contain wet cement because the weight of the load can cause muscle strains and back injuries. 3 zinc are not meant to support a person’s weight between the timber frame. Moving about this type of roof requires extra care because you need to walk along the lines of screws fixed to the timbers. First aid A building site should have a first aid box (Figure 1.2) which as a minimum contains: @ plasters; bandages; ointment; disinfectant. Someone on site should be in charge of the box and know how to deal with broken bones, burns and electric shocks. Working with bricks and blocks Working with bricks is not usually unsafe, but you need to be careful of your fingers and thumbs if you cut bricks with the sharp edge of a trowel. Concrete blocks are rough and heavy. The edges can injure your hands unless you wear gloves when you lift and carry them. If you do cut your hands, then you must clean the cut so that it does not become infected. Bandage Ointment Disinfectant Plasters Working inside a building It can be quite dark inside a building under con¬ struction. If there is no source of artificial light, then you need to be aware of the possible dangers. Holes for staircases and lifts must have secure barriers around them on upper floors to prevent anyone falling into them. Openings in external walls above ground level also need barriers to prevent people, equipment or materials falling through them. Working on roofs Safety measures for working on roofs include: 1. erecting scaffolding up to the lower level of the roof to save anyone who slips down a roof slope; 2. placing crawl boards to spread the load of the building worker’s weight when moving up and down the roof slope. Roofs built of materials such as fibre cement and Figure 1.2 A simple first aid box. Health^and hygiene Health and hygiene are as important as safety on building sites. This means that the workers should have access to an area for cooking and the facilities for basic hygiene as well as a schedule that allows rest breaks and meal times. Healthy workers need: ® shade for rest breaks; $ dry areas to prepare food and drink on rainy days; # facilities for washing hands; ® WCs; # areas to hang up wet clothes; # a room to change in and out of working clothes. 4 Building construction Safety notices Notices about wearing hard hats, avoiding acciden¬ tal fires or other careless activities can promote safe working practices. The site could have a no¬ tice board to remind everyone how many days or months it has been free from accidents. Explosive materials should be recorded on a register. • The site should employ someone who is ex¬ perienced at first aid. • A healthy building site will have adequate rest breaks and sanitation facilities. REVISION EXERCISES AND QUESTIONS CHECK YOUR UNDERSTANDING 1 A building site can be dangerous if you do not observe the health and safety regulations carefully. • You should always wear appropriate protective clothing when you are on site. A hard hat is essential when you work in ex¬ cavations or on scaffolding. Excavations should be inspected after heavy rain. 2 3 4 5 What are three pieces of essential protective clothing on a building site? Why should excavations be inspected after heavy rain? What steps should you take if someone re¬ ceives a serious electric shock? What are three dangerous materials that can be found on a building site? Explain what facilities make a healthy site. Introduction Buildings are the result of the need to provide an enclosed, secure space for people’s activities. In the short term a building can be constructed out of grass or mud on a timber frame. In the longer term, there is a need to use more expensive and durable materials. If more money is invested in the con¬ struction of buildings, then people will expect them to last a long time. The building industry has developed separate but related disciplines that employ people trained in building constaiction and technology. This chap¬ ter looks at the work of these people, who include: • the client; • the design team; • the contractor’s team; #5 the building material suppliers; • the regulators. The client A client with access to money and land is one of the most important people in a building project. When a client, who may be a private individual or a commercial organisation, decides to build, the process begins even before the first soil is turned. In many countries, the government is the main client for building projects that meet the basic needs of the people. Hospitals, schools and other public buildings are typical projects of this type. The design team The design team is responsible for the overall layout and appearance of a building. An architect Figure 2.1 Inside an architect's drawing office. may lead a design team, which consists of other architects and technicians. Figure 2.1 shows you the inside of an architect’s drawing office. Together the design team will produce: design drawings; ® working drawings; perspectives. During the building project the design team will also carry out administrative jobs and visit the site to observe progress and deal with problems that arise from the design or building work. The structural engineer The design team includes a structural engineer, who makes sure that buildings are structurally stable. You employ a structural engineer if the stresses and loads are greater than those in a simple house. 5 Building construction 6 The engineer calculates the weight of the con¬ struction materials, the weight of the people and equipment who will occupy the building and the maximum wind pressure on the building. These calculations enable the engineer to design: • foundations; • columns and beams; £ roof trusses; • suspended floors; • other structural elements of the building. When the structural drawings and calculations are produced, they are approved by the building inspector and used by the contractor on site. The quantity surveyor The quantity surveyor prepares a bill of quantities for building projects so that contractors can accu¬ rately price the work. The quantity surveyor works out the size of the areas and the volume of re¬ quired materials from the design team’s drawings and specifications. The clerk of works The clerk of works, who is usually employed by the client, is an expert in how buildings should be constructed. The clerk of works uses this knowledge to make sure that the contractor builds the building correctly and safely. The construction team The construction team is the term we use to de¬ scribe the builders who put up the building. This team consists of these people: £ main contractor; £ subcontractors; £ estimator; £ surveyor; £ contract supervisor; £ site agent; £ general foreman; trades foremen; £ tradespeople; £ apprentices; £ labourers. The main contractor enters into a contract with the client to build the building according to the design team’s drawings, specifications and bill of quantities. The estimator works out the cost of construct¬ ing the proposed building shown on the drawing and specification. If there is a bill of quantities, the estimator fills in the rates and produces the total cost for the job. This becomes the tender docu¬ ment which is offered to the client. The surveyor lays out the shape of the building on the ground before construction starts. The sur¬ veyor also checks the ground levels. The contract supervisor deals with the paper¬ work that may be required for large building projects. The site agent is the contractor’s representative on site for large contracts. The site agent’s job is to manage the site on a day-to-day basis. A general foreman is always employed on small contracts. The foreman should have exten¬ sive knowledge of all aspects of building construc¬ tion. This includes knowing how to organise the workers, materials and schedules. Trades foremen are experienced at specific trades such as brickwork, carpentry or plumbing. They organise and control the workers in their own trade. The trades foremen report to the general foreman. Tradespeople form the bulk of the construction team. They have spent years learning a trade, probably beginning as an apprentice to a skilled person, and obtaining the necessary qualifications to become recognised as an expert in their particu¬ lar skill, e.g, bricklaying, carpentry, electrical work, plastering, plumbing. Apprentices are building workers who are learn¬ ing the basic skills of a trade. Normally apprentices work with experienced people until they are cap¬ able of working alone. An apprentice may attend classes and work for a certificate while training for a specific trade. Labourers carry out the jobs on a building site that do not need special skills. These are usually physical tasks such as digging trenches and general cariying of materials around the site. Some trades also require labourers. Bricklayers use labourers to mix and carry mortar and to bring bricks and blocks to the place where they are working. The subcontractors Subcontractors, who are employed by the main contractor, do specific parts of the building project. They provide additional skills for the main con¬ tractor, who may not have q workforce that is competent in all the building trades. Subcontrac¬ tors run their own businesses and have the same responsibilities for the standard of work and safety issues as the main contractor. The building team Working together The design and building teams are involved in a construction project on and off the building site. Their work is to: 1. complete details on drawings; 2. make changes on site when required; 3. price the changes; 4. inspect the building work; 5. complete paperwork; 6. organise the right number and type of building workers; 7\ order equipment; 8. order the building materials. The technicians Technicians work for design or building teams. Depending on their experience and knowledge, they should be able to: 1. help to prepare working drawings; 2. interpret the drawings prepared by architects and engineers; 3. understand building construction techniques; 4. work on site efficiently; 5. understand building regulations; 6. apply health and safety rules to their work; 7. know how to operate equipment safely; 8. organise other building workers; 9- carry out work to a high standard. You can train to be a technician by: 1. attending a technical school or college to learn about building technology, construction methods and drawing; 2. working on building sites to see how to carry out building methods; 3. learning practical skills such as bricklaying, plumbing and carpentry in workshops. A good technician will also be aware of local climatic conditions and appropriate materials. This information promotes the comfort and health of the people who will occupy the building when it is finished. The building material suppliers Constructing a building takes people, materials and equipment. The building materials supply industry consists of the manufacturers and the builders’ merchants. The manufacturers make all the materi¬ als needed to construct the building. The builders’ 7 merchants buy the materials such as paint, cement, sanitary fittings and ironmongery from the manu¬ facturers and sell them to the building contractors. Contractors usually buy timber from merchants who specialise in different types and sizes of tim¬ ber. They buy sand and aggregates from quarries. Bricks and blocks are usually made locally at brickworks or block manufacturers. They may also be made on site by a contractor. The building industry regulators The regulators of the building industry protect the public and the building workers from dangerous and poor quality construction methods. The methods used to control building projects are a combination of inspections, legal requirements, good practice guidelines and the applications of research. Many countries have: building regulations; building codes of practice; research organisations who promote improved building methods and materials. In other parts of this book, we will refer to the building inspector. The building inspector plays an important role in the control of building projects. Normally, the building inspector, who works for a local authority, approves the working drawings for a proposed building. When the drawings are approved, the inspector issues a permit to build, which confirms that the design, layout and con¬ struction methods are acceptable. The planners The planners also control building projects be¬ cause they approve the overall design and position of a building. They are not usually concerned with the detail of a building design, but they want to make sure that the building will fit into the area. This means that the planners consider: • the type of proposed building; • the height of the building; the materials that will be used to construct the building; • access to the building. Buildings are permanent features of the land¬ scape in all countries. The planners want to control the way an area develops to make sure that it does not result in a confused mix of uses. 8 Building construction The planners will normally reject a proposal to build a factory in a residential area or to build a block of flats in an industrial area. Building types are usually divided into cat¬ egories and approved only for areas that share the same characteristics. Common categories are: domestic - houses, flats, hostels and hotels commercial - offices, shops, showrooms, markets industrial - factories, workshops, quarries public - cinemas, theatres, hospitals, churches, schools, colleges, universities agricultural - farms, ranches, small¬ holdings. Builders’ merchants usually supply the building materials. • Building inspectors are part of the control and regulation side of the building industry. They con¬ trol the construction, stability and health and safety methods. Planners control the overall design and siting of building projects. REVISION EXERCISES AND QUESTIONS 1 2 3 4 CHECK YOUR UNDERSTANDING 5 The client decides that a building is needed and employs the building and design teams. The architect, who is a key member of the design team, designs the building for the client. The other members of the design team are: the structural engineer; the quantity surveyor; the clerk of works. The building team works for the client, but follows the design team’s instructions. The main contractor constructs the building with assistance from subcontractors. The subcontractors are employed by the main contractor. Skilled technicians assist all parts of the building process. 6 7 What two things does the client need before issuing an instruction to an architect to design a building? How does the structural engineer help the architect on the design team? What is the relationship between the main contractor and subcontractor? What is the difference between planning con¬ trols and building regulations? Where does the contractor buy: i) paint ii) sand iii) timber? How many different categories of building use can you find in your own town or village? Find information about the climate in your area. i) Where does the wind usually blow from? ii) Which are the wet and dry seasons? iii) What are the maximum and minimum day and night temperatures? iv) What is the altitude of your home? v) What is the approximate latitude and longi¬ tude of your home? (Find this answer in an atlas.) Introduction One of the essentials for a construction project is the land that becomes the building site. Before the design work begins, you need to learn as much about the proposed building site as you can. You do this by: 1. considering the suitability of the site for its in¬ tended purpose; 2. investigating the site in person; 3. surveying the site; 4. digging trial holes. When this work is completed the information is used to prepare a survey drawing of the site. In this chapter we shall look at the typical steps that you take to complete the site investigations. With the exception of simple building projects, some or all of this work is usually carried out by a surveyor. Considering the suitability of a site Two factors affect a client’s decision to start a building project on a specific site: 1. its suitability for the purpose of the intended project; 2. the likely cost of developing the site. For example, sites used for housing or industrial activities need good access to transport facilities and other services. The plan for a town or a district may determine which types of building can be built in an area where the client has access to land. This means that the suitability of a site should be investigated before the design work begins. The client also considers the total costs of devel¬ oping a particular site before deciding if it is suit¬ able for a building project. A sloping site is more expensive to build on than a level site. Land that floods regularly or has poor soil conditions also costs more to develop. Investigating the site When the client identifies a site, then the building surveyor investigates it to find out the: 1. strength of the soil, because this affects the design of the foundations; 2. type of soil which will be excavated; 3. amount of water in the ground because this affects the design of the foundations and work¬ ing procedures; 4. amount of clean or contaminated ground; 3. amount that the ground slopes; 6. access to services such as mains water, electri¬ city and drainage; 7. best position for the building in terms of the local climate; 8. position of natural features such as trees, rocks and streams; 9. position of other buildings near the site; 10. location of site boundaries and access roads. A surveyor will dig trial holes to find out the condition of the soil and the amount of water present. Soil samples are removed and analysed. 9 Building construction 10 Surveying the site Part of the site investigation is the site survey for the design and working drawings. You can see in Figure 3-1 that a building surveyor uses survey instruments to do the survey. The surveyor finds out the horizontal and vertical levels to determine how flat the site is. Site levels are fixed in relation to a mark or level nearby such as: 1. a datum level mark, which is noted on survey maps (Figure 3.2) of an area as the height above standard sea level in metres; 2. a manhole cover in a nearby road, which is a permanent marker for ground level; 3. a mark made on a rock face or tree, which can be measured and used to establish levels when the building work begins on site; 4. spot levels, which are points marked out on the ground for taking levels. Drawing up the site survey When the survey is completed the information is used to prepare a drawing to a suitable scale to show the physical characteristics of the site and the area around it (Figure 3-3). mm Figure 3.1 Surveying a building site with instruments. The site investigations Figure 3.3 A site survey drawing with contours. 11 Building construction 12 The drawing includes: 1. the shape and size of the site in relation to the area around it; 2. the building line. This line is usually the dis¬ tance that must be maintained between the proposed building and the site boundary. The building inspector can confirm whether the build¬ ing line is correct. 3. the datum level that served as the baseline for the survey levels; 4. the location of any spot levels on the site; 5. the contours, or lines that show the amount and direction of any slope on the site; 6. road access to the site; 7. the location of any manholes and the direction of the drainage runs. This should be confirmed with the local authority, who may also give you information about the direction of flow and invert levels. 8. the location of any sendees such as water and electricity in relation to the site; 9. the position of trees or other natural features which might influence the building design or construction work. • A site survey uses measuring equipment to es¬ tablish the horizontal dimensions and the vertical differences in levels on the site. • The datum is a level that is marked on maps to provide a common fixed measurement such as the height above sea level. $ Spot levels are the series of points on the ground where the surveyor takes the levels. • Contours are lines that join points of equal height above or below the datum level. They show the direction and height of a slope. • A survey drawing is a scale drawing that shows the physical features, dimensions and levels of a site as well as any known conditions below the ground level of the site and adjacent proper¬ ties. REVISION EXERCISES AND QUESTIONS 1 2 3 CHECK YOUR UNDERSTANDING Site investigations require examination, meas¬ urement and recording of the physical features of the proposed site and adjoining sites and proper¬ ties. Trial holes are used to investigate the condition of the soil below ground level. 4 5 Which factors are likely to increase building costs? Which three services are useful for site develop¬ ment? What feature indicates the presence of drains below ground? Draw the outline of the building you are sitting in now. i) Show north and the other points of the compass on the drawing. ii) Show the location of any manholes beside your building. Find the approximate location of your building on a survey map. Introduction The production of the construction documents is as important as the organisation of people and materials in a building project. This chapter de¬ scribes the functions of the main construction docu¬ ments, such as the: • working drawings; # specification; 9 bill of quantities. plans, sections and elevations of a building. The working drawings are drawn to a suitable scale and indicate the location and shape of the building and its structure. The working drawings are the basic documents that are used by the main contractor and sub¬ contractors on site to construct the building. They may also be used for other purposes such as: 1. obtaining planning and building control approval from the local authority; 2. preparing the specification of work; 3. preparing a bill of quantities; 4. preparing a tender estimate for the project. The working drawings The plans, sections and elevations After the building is designed, the working draw¬ ings are produced. Prepared by the architect or the architectural technician, they show the detailed The working drawings consist of plans, sections and elevations. ^ Manhole \ Figure 4.1 An example of a ground-floor plan for a house. 13 14 Building construction V u 1 JF L V ■It 1 Figure 4.2 The elevation of a house. The site plan shows the relationship of the building to the site boundaries and adjoining roads and buildings. The floor plans show the position of the walls, partitions, doors and windows, as you can see in Figure 4.1. The roof plan shows how to place the timbers to form the roof. The four elevations are the external views of the building; they show the general appearance and where to put the doors and windows. Figure 4.2 shows an example of an elevation. The sections show the depth of the foundations and the levels of the floors and roofs. The sections may include other construction details (Figure 4.3). The foundation plans show how the building should be set out on site and the dimensions of the strip foundations for the load-bearing walls. Figure 4.4 is an example. Additional drawings may be prepared to show specific details to a larger scale. With practice in reading drawings, you will become familiar with the symbols. Symbols on working drawings Working drawings use symbols to show the differ¬ ent materials specified in the construction of a building. These symbols are common to all draw¬ ings so that everyone on the building team can interpret them correctly. The most familiar symbols are listed in Figure 4.5. The specification The specification is a document that describes the standards of workmanship and materials required 15 The construction documents Raft foundation for the verandah *1 f T 15 Pad foundation for the piers r i i I Foundation for the fireplace i—i & k—^-• 10 Strip foundations for load-bearing walls rT_. J L I Figure 4.4 A foundation plan. 0/ y y Brickwork sections ■:o. K /I ii ii ii ii i Cavity wall section Blockwork sections Stone sections y Mass concrete Figure 4.5 Symbols on working drawings. Reinforced concrete Cement and sand screed 16 Building construction for a building project. The design team writes the specification, which also describes the sizes and shapes of the different parts of the building struc¬ ture such as the windows and doors. Sample specification This is an example of a specification for a building’s foundation. 1. Supply and lay the hardcore bed in layers 150 mm thick, well consolidated to the thickness shown on the drawings or as required to make up any additional exca¬ vation. 2. Supply and lay minimum 50 mm of sand blinding to the top of the hardcore to provide a firm and level surface for the dpm and the oversite concrete slab. 3. Supply and lay over the whole area of the ground floor on the blinding provided, 1200 gauge polythene dpm. Provide 150 mm laps at joints and overlap the dpc in the walls. Ensure that there are no tears in the sheeting and that the dpm and the dpc together provide a complete damp-proof barrier. 4. Mix, transport, spread, consolidate and level the 100 mm oversite concrete, mix 1:2:4, carefully over the polythene dpm. Finish with a tamped finish to receive the floor screed and cure for at least seven days. The bill of quantities The bill of quantities allows the contractor to price the work accurately for a large job. The quantity surveyor reads the working drawings and specifi¬ cation to determine the volumes, areas and linear amounts of work required. When these are written up as the bill of quantities, the contractor decides how much to charge for each part of the job and adds this up to determine the total price of the building work. The contractor then adds an amount for overheads and profit to the price for the materials. If contractors compete for a building project, the use of a bill of quantities ensures that they all price for the same amounts of materials. Figure 4.6 shows what a sample portion of a bill of quantities looks like. BILL No. 3/ FOUNDATIONS Unit Qty. Rate Amount (J) 65/A. Hardcore well watered, rolled and compacted in layers not exceeding 150 mm M3 9 t 4-1.00 t 37Z- OO 65/B. 50 mm thick sand blinding M2 60 112.-OO t 72o. OO 65/C. 1200 gauge polythene damp-proof M2 60 \ l% oo t I0$0. OO M2 60 1130.00 t ?xoo. oo membrane, with 150 lap joints & incl. 150 overlap to dpc at perimeter 65/D. 100 mm thick 1:2:4 concrete class B25 laid flat and including tamped finish to receive floor screed (measured elsewhere) V 874/TECHNICAL COLLEGE Page 65 Figure 4.6 A sample page from a bill of quantities. To collection FOUNDATIONS I W8\ OO 17 The construction documents CHECK YOUR UNDERSTANDING • Working drawings are produced by the archi¬ tect’s office. • Working drawings show the plans, elevations and sections of a building. $ The plans show the view of the building’s shape and position on the site as well as the details of the construction of parts of the building like the roof and floor. © The sections are the drawings that show the details for the internal parts of the building like the foundations and the floors. Q The elevations are the views of the outside of the building, which show the position of doors and windows. $ The working drawings provide the contractor with information about the dimensions, levels and general layout of the building and services. 9 Working drawings are needed for permission from the local authority to proceed with the pro¬ posed building. 9 The specification describes how to do the build¬ ing work. 9 The bill of quantities describes the amount of materials needed to construct the building. REVISION EXERCISES AND QUESTIONS 1 2 3 4 5 6 What is the purpose of a site plan? What documents are needed for approval for building construction? What is a plan, section and elevation? What is the difference between a specification and a bill of quantities? Can you draw a plan of a rectangular building which is 12.5 m x 7.8 m to a scale of 1:100? A contractor prices the following items in the example of a bill of quantities in Figure 4.6: Item i) hardcore ii) blinding iii) polythene iv) concrete Rate * 50/m3 * 120/m2 * 73/m2 *215/m2 Can you work out how much each quantity costs and add up the total cost for each item? (* represents your own currency) Introduction The contractor’s site preparation begins after the: 1. building has been designed; 2. construction documents have been approved; 3. main contractor has been appointed by the client to construct the building. When deciding how to prepare for the building work, the contractor will frequently refer to the working drawings and specification. This chapter describes the site preparation in detail from the contractor’s viewpoint. The contractor’s responsibilities The contractor is expected to carry out the building work: using appropriate knowledge, experience and skill; $ efficiently and without delay; employing skilled technicians and building workers in the different trades; @ using the most appropriate materials; ® ensuring that health and safety regulations are observed; giving the necessary information to the local authority when required. Figure 5.2 Access gates with vision panels. Setting up the site One of the contractor’s first jobs is to lay out the site boundaries as they are marked on drawings such as shown in Figure 5.1. If a security fence is put up around the site boundaries, the contractor can control the move¬ ment of people and materials (Figures 5.2-3). 18 Ideally, the boundary fence should have a single access point so that someone can check people in and out. This ensures that only authorised people Preparing the site 19 20 Building construction are on site and that personal effects can be left safely. A temporary access road should be constructed so that vehicles can enter the site in all weather. You can see an example of a temporary access road in Figure 5.4. This access road can become part of the permanent site services in the final design. Site requirements A well-managed site should have these facilities and services: 1. A site office with secure storage and workshops. 2. A toilet. It may be chemical or connected to mains drainage. 3. A supply of fresh water for drinking, washing and the building work. If water is not available from the mains supply, then a storage tank should be filled from time to time. 4. An electrical supply for power tools. Electricity can be supplied from the mains or a petrol generator. 5. A telephone, which is secured so that it is only used for authorised calls. 6. Space for storing materials and machinery. Cement should be kept in a dry, locked store. Figure 5.4 An urban building site. 7. A contractor’s name board, which is useful for publicity and to identify the site for deliveries. The temporary site buildings and facili¬ ties should not be too close to the building that is being constructed. Clear space must be left around the building for dumping excavated earth and moving machinery and materials. The concrete mixer should be left in a permanent location during the building work. Deliveries of aggregates will need clear access to the concrete mixer. Tools and equipment A variety of tools and equipment is needed to do the digging, lifting, fixing and measuring jobs that are part of the work on a building site. A basic list should include these items: 1. a tool for slashing through scrub; 2. a tool for hand excavation; 3. a pick for breaking up hard ground; 21 Preparing the site 4. an axe for chopping down trees; 5. a spade for shifting sand and aggregates; 6. a sledgehammer for breaking up rock; 7. a wheelbarrow for carrying materials around the site; 8. wooden pegs for marking out and fixing lines; 9. hammers and nails for fixing timber; 10. a 3 metre tape measure for measuring short distances; 11. a 30 metre tape measure for setting out boundaries; 12. line for stretching between pegs; 13- levelling instruments and pegs for setting out vertical levels; 14. a builder’s level for checking horizontal and vertical levels; 15. a plumb-bob for checking vertical levels only; 16. a crowbar for levering heavy materials; 17. a builders’ square for making right-angled corners. The ground around a termite nest is usually treated with toxic chemicals. For this reason, you must take great care when you handle the chemicals. It is advis¬ able to wear gloves and goggles to prevent the inhalation of fumes. The chemicals and powders should be mixed in the open air. Trial holes A contractor will dig trial holes as part of the preliminary site works. These holes provide infor¬ mation about the best methods of excavation. For example, if water appears in the trial holes, then the contractor may use pumps to keep them dry while the building workers are digging. If the soil is veiy loose, then the contractor will want to put in timber supports to strengthen the sides of the excavation. CHECK YOUR UNDERSTANDING Clearing the site The preliminary site works for a construction project usually begin after the site facilities are set up. Clearing the site is essential. First, all vegetation such as bushes and scrub should be removed. The roots of trees and bushes must be dug out and cleared away. The site needs to be clear of rocks and boulders in the area where the building will be set out. If they are too large, then the boulders or rocks must be broken into smaller pieces and taken away. Site clearance is done by a combination of manual and mechanical methods. These methods are de¬ scribed more fully in Chapter 7. Work should begin after official permission has been given by the local authority. The working drawings and specification should contain all the information that the contractor needs to complete the building. The contractor must have the right experience to do the job. The site should be prepared before the work starts. Temporary buildings should be put up for the building workers to use. A complete inventory of the tools needed for building work is useful. The concrete mixer and aggregates should be carefully sited. @ Termite nests on the site must be destroyed. The soil condition should be checked before excavations begin. Clearing termites The building site and surrounding areas should be inspected for termites as part of the process of clearing the site. Termites present a danger be¬ cause they eat the cellulose in the timber in build¬ ings where they cannot be seen. Destruction is often well advanced before it is obvious on the surface. To remove this danger, the termite nests must be dug out and the contents destroyed. REVISION EXERCISES AND QUESTIONS 1 2 What is the purpose of the working drawings and specifications? What are three responsibilities of the main contractor? 22 3 4 5 Building construction How can a contractor ensure vehicular access to the site during the rainy season? Why should termite nests be destroyed on a building site? Why should the contractor dig trial holes be¬ fore work begins? 6 Figure 5.1 shows a building site and the loca¬ tion of the proposed building. Draw this to a 1:100 scale and show suitable locations for the contractor’s huts, equipment and materials. uilding Introduction After the site is cleared of obstructions the outline of the building can be set out on the ground with fixed lines and profiles. This chapter describes how to set out the outlines on the ground for square, rectangular and circular buildings, Setting out the building outline Table 6.7 How to set out a building Step 1 2 Action Assemble the equipment for setting out: the working drawings; sharp pegs which measure 75 x 75 x 300 mm; a mallet to drive the pegs into the ground; a hammer and nails; a ball of string to create the outline; a builder's square; a 30 metre steel tape measure. Find out the distance from the site boundary to the building line on the working drawings. Use the tape measure to measure the same distance from the site boundary to the location of the building line on the ground. Select a corner on the ground to be corner A. 3 Place a peg in the ground at corner A and hammer a nail into the top of the peg. 4 Repeat these steps to place a peg in the ground for corner B. 5 Tie the string between pegs A and B. Measure the distance between A and B. Check that the distance on the ground is the same measurement as the distance on the drawing. 6 Repeat these steps for corners C and D. 7 Measure the diagonals A-D and B-C (the two diagonals should be equal). 8 Use the builder's square to check that the corners are at right angles. Table 6.1 describes how to set out the corners of a square or rectangular building. Figure 6.1 will give you more information about setting out a building. Making right angles The walls of a square or rectangular building must form right angles of 90°. The traditional method for making right angles is to use a 3-4-5 triangle. Table 6.2 describes how to make and use a 3-4-5 triangle. Table 6.2 Using a 3-4-5 triangle to make right angles Step Action 1 Nail three pieces of timber together which you cut to these lengths to make a frame 750 mm 1000 mm 1250 mm A frame with a right-angled corner Is called a square. 2 Place the right angle of the square against the lines between the corners. If the corners are not at right angles then move the corner pegs until they make right angles. 3 Measure the diagonals to check that they are the same length. 23 24 Building construction Figure 6.1 Setting out the corners of a building. Another method of making right angles You can also make right angles with string and three pegs. You can see what this looks like in Figure 6.2. Follow these simple steps for making this type of right angle: Cut a piece of string that measures 3600 mm exactly after a loop is tied in each end. Attach both loops over a nail in the first Figure 6.2 Making a 3-4-5 triangle with pegs and string. pegStretch out the string ^nd place a second peg 900 mm from the first peg. Place the third peg 1200 mm from the first peg and pass the string around it. 25 Setting out the building Fixing the corners in place Table 6.3 Making and using profiles Step The position of the corners must stay fixed in place after the ground is excavated. You will need to build special boards called profiles to attach the lines that define the outline of the building. The profiles replace the corner pegs. A profile consists of two timber posts with a horizontal board across the top. The posts are sharpened like stakes so that they will stay in the ground. You should use two profiles at each cor¬ ner. This means that you must make eight profiles for a simple rectangular building. Figure 6.3 shows you what the profiles look like and how to place Figure 6.3 Locating the profiles. Action 1 Attach a horizontal board to two timber posts and sharpen the posts at one end to stick in the ground. 2 Mark the top of the board with nails to show the width of the walls and foundations at the corners. 3 Place a pair of profiles in the ground beside the pegs used for setting out and check that the angles are still 90°. 4 Stretch lines between the profiles at the corners of the building. Use nails to locate the position of the walls and foundations. 26 Building construction them. Table 6.3, on page 25, describes in more detail how to make and use profiles to fix the building lines. When the profiles are fixed, then you have completed setting out the horizontal levels of a building with right angles. The profiles should remain fixed in place until the building work is finished. Setting out columns and piers Columns and piers, which are upright supports, should be set out on two lines that pass through Figure 6.4 Setting out columns. the centre of the column or pier at right angles to each other as you see in Figure 6.4. You should follow these steps to set out col¬ umns and piers: 1. Locate the positions of the columns or piers on the working drawings. 2. Measure the positions on the ground and place pegs to mark the centre of the columns or piers. 3. Check that the lines are at right angles to the proposed wall positions. 4. Run lines from the centre of the pegs in both directions to the opposite wall positions or profiles. 5. Remove the pegs as the building work progresses. Setting out the building 27 Setting out circular buildings Circular buildings need profiles that move. Table 6.4 describes how to set up a moving profile. Table 6.4 Setting up a moving profile for a circular building Step Action 1 Find out the radius of the building from the working drawings. 2 Mark out this measurement on the ground. 3 Place a stake securely in the ground at the end of the radius in the centre of the building. 4 Drill a 12 mm hole in the stake. 5 Place a 12 mm reinforcing bar in the hole in the Stake. 6 Check that the top of the bar is level. 7 Cement the stake in position. 8 Loop a piece of rope which is the length of the radius of the building over the reinforcing bar. Measure the distances to the inner and outer sides of the foundation from the working drawings. Use the rope to measure the same distances on the ground. Mark the distances around the outline of the building. After you measure the radius and position the stake, then you can place a 12 x 150 mm board over the reinforcing bar. This method can be used instead of setting out with rope. The board is called a trammel. Figure 6.5 has a drawing of a trammel. You should measure the width of the foun¬ dation and masonry walls and mark the top of the board for further use. Setting up a site datum for vertical levels Before work begins the contractor needs to find a fixed point to measure the different levels of the building. This fixed point, which can be a wooden peg, is called the site datum. Typical levels that need to be measured as you can see in Figure 6.6 are: 1. the depth of the foundation trenches; 2. the height of the concrete strip foundations; 3. the depth of the excavation under the hardcore bed; 4. the height of the hardcore bed; 5. the height of the oversite concrete slab. Trammel board Outline of wall Figure 6.5 Setting out a circular building. Figure 6.6 Detail of a datum in relation to the foundations. 28 Building construction When these levels are established, then you can measure other levels (see Figure 6.7) such as: 6. the bearing for ground-floor timber joists; 7. the bearing for first-floor timber or concrete floor construction; 8. the bearings for roof trusses, rafters and wall plates; 9. the heights of window cills and lintels. Table 6.5 describes how to set up and use a site datum for the building levels. Table 6.5 Setting up and using a site datum Step Action 1 Select a position for a wooden peg where it will not be disturbed by building work and place it so that the top is about level with the top of the oversite concrete slab or other fixed level. 2 Set up the survey levelling instrument so that you can see a measuring staff on the concrete slab and the site datum mark. 3 Level the site datum mark and concrete it in position (Figure 6.8). Floor level Bearing for joist hanger Head of door Floor level Joist bearing level Datum Site datum peg Figure 6.7 Establishing levels above and below the site datum. Setting out the building 29 A 3-^-5 triangle is a check that the lines are square. The diagonals must be the same length, f Fixed profiles for right-angled buildings should be placed where they will not be disturbed by the building work. • A moving profile or trammel can be used to set out curved walls. • Centre lines are used to position columns or piers. A site datum can be used to fix vertical levels. REVISION EXERCISES AND QUESTIONS 1 Figure 6.8 Detail of a site datum. 2 3 CHECK YOUR UNDERSTANDING 4 # The site must be cleared before construction begins. $ The position for a corner of a building must be set out first. # A right-angled base line must be established for the positions. 5 If the shortest side of a 3^-5 triangle is 750 mm then how long are the other two sides? What should you do if the diagonals are not equal when you check the setting out? Make a right angle using three pegs and a length of string. Using bricks, set out the inner and outer walls of a circular building which has an internal diameter of 5 metres and a wall thickness of 215 mm. Describe how you would set up a site datum mark. Introduction The site must be excavated to build the founda¬ tions below ground. Excavation is normally done by hand or with mechanical diggers. At this stage, the contractor already has two important sources of information about excava¬ tions: 1. the trial holes, which revealed the type of soil under ground; 2. the working drawings which indicated the depth required for foundations. Workers on small building sites usually carry out these types of excavations: Figure 7.1 A site after the topsoil is removed. 30 1. removing the top soil; 2. reducing levels to make an even working surface; 3. digging trenches for strip foundations; 4. digging pits for pier and column bases; 5. digging holes for piles; 6. digging into sloping sites; 7. digging stepped foundations; 8. digging out basements. The contractor must solve two problems that affect the safety of the workers digging an ex¬ cavation: 1. supporting the sides; 2. removing water. 31 Excavations It is very important to take special precautions when workers are digging below ground. Removing the topsoil Topsoil should be removed because: 1. it contains vegetation, which can damage foundations; 2. it is not firm enough to support a building. You should remove at least 300 mm of topsoil. If you have to remove the roots of bushes and trees that are growing within the boundary of the building, then you may have to excavate more than 300 mm. Do not use soil to backfill holes that are created by excavating roots in the topsoil. The soil may settle to a different level in the holes and create cracks in the oversite concrete. You should pack hardcore tightly in the holes or use a weak concrete mixture for a filler. If you do not use the topsoil to landscape other parts of the site, then it should be cleared away. Figure 7.1 shows you an example of a site after the topsoil is removed. Excavating the subsoil When you remove the topsoil, then you should have a firm subsoil that is strong enough to sup¬ port the oversite concrete. 1. Use the working drawings to see how deep the hardcore bed should be. 2. Dig down past the topsoil to the recommended level in the subsoil. 3. Inspect the ground to check that the subsoil is firm. 4. Dig out any soft patches of ground and fill with tightly packed hardcore. This work can be done manually with: @ spades;. ® shovels; ® pick-axes; # wheelbarrows. Mechanical equipment makes the job much easier. A bulldozer can quickly push the topsoil Figure 7.2 Reduced levels after removal of the topsoil. out of the way for later disposal. You can reduce levels with a mechanical shovel and load the exca¬ vated material directly onto a tipper truck for re¬ moval. Figure 7.2 shows you how the reduced levels should look when the topsoil is removed. Digging a trench for strip foundations You may need to dig even deeper into the subsoil to excavate trenches for strip foundations. (See Figure 7.3 as an example.) The depth of excavation for the trenches will be on the working drawings. Excavation by hand, using spades and shovels, is a good method for excavating trenches for the foundations for small buildings. If you want to achieve more speed then you can use a backacter. This is a particularly good piece of machinery to use if the trenches are quite deep. You can use two methods to check that the excavation is deep enough. Use a levelling instrument to check the depths of the trench against the site datum. (Figure 7.4.) Use a boning rod to measure the depth of digging. Table 7.1 describes how to do this correctly. The deeper the excavation the more it costs to dig and to fill with concrete. Although the concrete will smooth out any differences in depth, it is more economic to be accurate. 32 Building construction Figure 7.3 Excavating a trench for a strip foundation. Figure 7.4 Using a survey instrument to check the depths of a trench. Table 7.1 Using a boning rod Excavated soil should be removed from the trench. You can use some of the excavated soil to fill in around the foundation brickwork, but the rest should be removed from the site. After the excavation is completed the building inspector may want to check that the subsoil in the bottom of the trench will support the building load. Excavating pits for columns or piers The excavation for the base of a column or pier is called a pit Pits are usually square. You mark a Step Action 1 Calculate the depth from the top of the profiles to the desired level of the excavation. Use the working drawings and measurements on site. 2 Make a measuring staff called a boning rod which is the same length as the distance between the top of the profiles and the bottom of the trench (Eigure 7.5). 3 Place the boning rod in the trench. 4 Dig down until the top of the 'T' on the boning rod lines up with the top of the profiles. 33 Excavations position and dig around the central point of the column or pier. You can dig pits by hand or use a backacter. Any water should be removed, and the sides of the pit should be supported if there is any doubt about their stability. hole reaches the depth required to support a build¬ ing load. Augers can be turned by hand or by machine. Manual augers are usually suitable for small jobs. Bigger and deeper piles require mechanical augers, which are mounted on machines. Digging holes for piles You will usually use a short-bored pile for small buildings. They are circular concrete columns formed in holes in the ground. . You use an auger, which is a spiral-shaped hand tool, to drill a hole in the ground. As it rotates, it drills down into the soil. When you pull out the auger, it brings out the soil with it, creating a circular hole. You repeat the process until the If you need to put in piles, then the ground should be soft enough to drill into with an auger. Digging into sloping sites Most building sites are not perfectly level. The design for a sloping site may have different floor Sight line between profiles r Depth of Boning rod excavation below profiles All profiles are set at the same height above the datum Reduced level m — $> Site datum V w n Depth of excavation below the datum P Profiles Figure 7.5 Establishing the depth of an excavation using a boning rod. 34 Building construction levels or a basement to cope with the changes in levels. You use the cut and fill method of excavation if you want to keep a level ground floor in spite of a slope. In this method the soil from the upper part of the slope is cut out and deposited on the lower part of the slope. This creates a level base for the construction of the floor. The base must be well packed so that the building is stable. Excavating foundations in rock You normally do not need to build foundations in rock because a rock base is strong enough to support small buildings. If the rock does not provide a level base for the walls, then you may need to make a concrete levelling strip in the rock. For rock that is 300 to 400 mm below the surface this requires: 1. the removal of the topsoil: 2. the excavation of a strip foundation trench. Digging a basement on a sloping site You may want to make a basement in a house on a sloping site or build retaining walls to support the sides of the remaining slope near the building. To successfully dig a basement on a sloping site, you will need to: • reduce the pressure from the ground on the vertical wall at the back of the house. Normally you would ask the advice of a structural engineer and then build a retain¬ ing wall; # provide a damp-proof membrane (dpm) between the soil and the adjacent wall. The dpm should be asphalt. Figure 7.6 illustrates the excavation for a foun¬ dation for a basement. If the rock is at ground level, then you need to pour the concrete into timber formwork above the ground. You must drill holes into rock foundations and insert reinforcing bars to make sure that the concrete levelling strip does not move. Supporting the sides of an excavation The contractor needs to assess how long an exca¬ vation can safely remain open without support for Figure 7.6 Excavation for a basement on a sloping site. 35 Excavations Wedge Working space between the struts Trench support for non-cohesive soil ■ N Concrete strip foundation & Concrete strip foundation Figure 7.7 Supporting the sides of an excavation. the sides. If the weather is very dry then the lack of moisture may cause the soil to shrink, crack and fall in. If the weather is very hot then the sides of the excavation may be unstable. In both these cases, it is better to provide timber supports for the side walls. Figure 7.7 illustrates how to do this. As a rule the looser the soil the more it needs to be supported. Example: excavations in sand and gravel soil should always be supported. Excavations on a confined site may also need support in case heavy loads are placed or driven too close to the edges of a trench or pit. The lives of the workers digging in the excavations are at risk unless the contractor takes proper precautions. Timber struts which are wedged between planks support the sides of the excavations. These sup¬ ports consist of: 1. polings, which are vertical planks supporting the soil. In sand or gravel, they should be placed close enough together to form a continuous timber wall. Depending on the soil type and working conditions, they may be placed about 900 mm apart. The purpose of the polings is to keep the soil on the sides of the excavation from falling in; 2. walings, which are horizontal timber strips sup¬ porting the polings; 3. struts, which are timbers that span across the trench between the walings. The struts hold the opposite walls of the excavation in place; 4. wedges, which are pieces of timber used to maintain the pressure of the polings against the soil. If the soil expands or shrinks while the work is carried out, then you may need to adjust the wedges again. Finding water in excavations A trial hole may show that water is normally present in the ground on site. The level of water in the hole is called the water table. It varies according to the seasons and the amount of rainfall. 36 Building construction (f) Figure 7.8 Mechanical plant used in excavations (a) bulldozer; (b) mechanical shovel; (c) backacter; (d) dump truck; (e) mechanical auger; (f) pneumatic drill; (g) tipper truck. Excavations Water also enters excavations when it rains. If the rainwater does not drain away naturally, then you should pump it out so that work can continue in the excavation. You can pump water out of excavations with electric or petrol pumps. If you use a pump, then the end of the hose line should be below the bottom of the ex¬ cavation in a small depression (called a sump). The hose should have a filter to prevent dirt from coming up into the pump. If you remove the water by hand, then you must dig a sump that is large enough for a bucket. When the water is removed it should be drained away so that it does not run back into the excavation. Excavation plant Mechanical excavation plant can be used for most excavation tasks. Some machinery can do more than one task. This section describes the different types of mechanical plant used for typical excavation work. They are illustrated in Figure 7.8. Removing the top soil and reducing the levels This work is done by: 1. bulldozers, which push the soil layer by layer to one side and pile it up nearby. A bulldozer does not dig out or lift out the soil; 2. mechanical shovels, which take off layers of soil in buckets. A mechanical shovel can be raised, lowered or tilted to deposit the earth into a tipper or dump truck and removed elsewhere on site. Excavating trenches You can use a backacter for this type of excava¬ tion. A backacter digs down with a bucket on a jointed boom and scoops the soil towards itself. Since the bucket is narrow it is useful for forming trenches. The backacter can also deposit soil on trucks or dumpers. A trench that is dug out by a backacter will usually need to be finished off by hand. 37 Digging pile holes A mechanical auger digs pile holes. This piece of equipment is a large drill mounted on a platform. The auger drills a hole in the ground and lifts out a column of soil. Drilling rock A hand-held pneumatic drill will drill into solid rock. The drill is connected by a hose to a com¬ pressor that provides the power. Removing soil Two types of truck are used to remove soil from an excavation. They are the: 1. dump truck, which is used for many jobs on a building site, including the movement of soil over short distances. The body of the dump truck tips forward and deposits the soil in the required position; 2. tipper truck, which is a road vehicle used to remove large amounts of excavated material to locations away from the site. The body of the tipper truck tips up and empties the soil at the back of the vehicle. Working safely in excavations Chapter 1 describes in detail the safety measures that you should follow when working in excava¬ tions. This section reminds you about the basic rules. ▲ The most important rule is to make sure that the sides of the excavation are always supported. The collapse of the sides of a trench or hole can cause injury or death. You should always look at these factors when you are working in or close to excavations: 1. Is the soil firm or loose? 2. How long will the excavation be left open? 3. Is the rainfall excessive? 4. Are the temperatures very high? High tempera¬ tures can dry out the soil. 5. How deep is the excavation? A deep trench needs more support for the sides. 6. Are there heavy loads or vehicles near the edges? 7. Is there any vibration from nearby equipment? 38 Building construction Workers should wear: strong boots with reinforced toecaps; protective helmets; gloves; waterproof boots in wet conditions; goggles when working in rock. CHECK YOUR UNDERSTANDING REVISION EXERCISES AND QUESTIONS 1 2 3 4 Excavation is used to remove soil to lay a foun¬ dation or to reduce the levels below an oversite slab. Excavation can be done with machines or by hand. The amount of support required in an excava¬ tion depends on the strength of the soil. Timbers are used to provide temporary support to the walls of an excavation. Water can fill excavated holes and trenches, which is dangerous. Safety is very important in excavation work. 5 6 Draw and label the timber supports for a trench. What are the advantages of these excavation methods on a sloping site: i) cut and fill ii) stepped foundations? Why should foundations be built below ground level? Why should you remove topsoil before digging the foundations? Which type of mechanical equipment do you use for: i) clearing a site ii) digging narrow trenches for foundations iii) removing soil from an excavation and de¬ positing it nearby? Describe how you would use boning rods to establish the correct levels of foundations. Introduction The foundation is the part of the construction where the base of the building meets the ground. Foundations are usually placed below ground level because the surrounding ground provides: 1. stability; 2. protection against impact; 3. protection from the extremes of weather such as excessive rain or drought. Although the depth will vary according to the conditions on site, the best load-bearing ground is normally 900 mm below the surface. Foundations are divided into two types: 1. the natural foundation This is the ground underneath the base of the building after the excavations are completed; 2. the artificial foundation. This is the structure that lies between the building and the natural foundation. This chapter looks at different types of founda¬ tion and the principles behind their design. Foundation loads An artificial foundation transfers the loads from the building to the ground. This prevents settlement or building movement, which might cause instability and endanger the occupants. The strength of the natural foundation must be greater than the pressure from the building loads on the artificial foundation. An artificial foundation carries the building loads which you see in the example in Figure 8.1: 1. dead loads These are the weights of all the fixed parts of the building such as the walls, floors, roofs, ceilings and services such as sani¬ tary fittings and plumbing; 2. superimposed or live loads These are the weights of the people, furniture and machines that will occupy the building after completion; 3. wind loads These are the pressures on the walls and roof from the wind. The pressure from wind loads on foundations is more important in tall buildings. These building loads place the most pressure at the bottom of the building, where the artificial foundation is located. For this reason, you need to choose the type of artificial foundation that suits the local ground conditions. Conditions that affect foundations You should consider the following conditions when you choose the correct type of foundation: 1. the load-bearing capability of the ground; 2. the depth where you will find suitable loadbearing soil; 3. the distance from trees which can affect the stability of the soil; 4. the level of the water table; 5. the normal variation in the water table; 6. the total weight of the building. If the building is heavier than the soil that was removed, then there will be some settlement as the soil adjusts to the new load. Figure 8.2 shows you some examples of these conditions. 39 40 Wind direction Building construction Roof construction: dead load Wind load Water tank: dead load Person: live load Furniture: live load Floor construction: dead load Wind pressure -► Wall: dead load Artificial foundation: dead load Figure 8.1 Loads on natural and artificial foundations. 41 Foundations Choosing the correct type of foundation The choice of foundation depends on: 1. the strength of the natural foundation; 2. the weight of the building and its loads. The natural foundation must be able to carry these loads with a minimum of movement. This capacity depends on the type of soil and the amount of water in the soil. See Chapter 22 for more information on tests for soil load-bearing capacity. The artificial foundation lies between the natural foundation and the building. Its purpose is to: 1. transfer the building loads to the soil; 2. spread the load evenly across soil that can sup¬ port the load. Although concrete is the preferred material for the construction of the artificial foundations, the form will depend on the specific conditions of the building and environment. Simple checks for the correct foundations You can use these simple checks to choose the correct type of foundation for small buildings. The alternative is to carry out soil testing and to calcu¬ late the specific building loads. Check that: 1. The foundations do not rest on made-up (previ¬ ously used) ground (Figure 8.2). 2. The subsoil is a consistent texture. Hard or weak spots will cause uneven settlement of the build¬ ing, which can create cracks in the walls. 3. Walls are centred on the strip foundations. 4. The foundations are wide enough. 3. The concrete thickness is at least 130 mm. 6. A higher foundation projects over and meets a lower foundation for a minimum distance of 300 mm on sloping ground. Made-up ground Types of foundation Many small buildings are constructed with loadbearing walls on strip foundations. You may find that the soil condition requires an alternative type of foundation. These are the different types of foundation that you can use: ® concrete strip foundation; ® deep strip foundation; Figure 8.2 Ground conditions. 42 Building construction raft foundation; piled foundation; pad foundation; stepped strip foundation. Table 8.1 The minimum concrete mix for foundations Parts of the mixture Weight 1 bag of cement 50 kg 0.1 m3 sand 160 kg dry sand 0.2 m3 aggregate 288 kg Concrete strip foundations used most frequently. They consist of continuous mass concrete strips poured in the bottom of trenches. These foundations will support loadbearing walls which are centred on the concrete strips to spread the pressure from the walls, roofs and other floor loads evenly. The concrete strip is usually a uniform width and depth. The foundation must be wide and deep enough to avoid soil movement that could cause instability. Depending on soil conditions, the maximum depth may be 900 mm. Building regulations may suggest the suitable minimum width for strip foundations. The concrete must be at least as thick as its projec¬ tion from the base of the wall. This ensures that the pressures of the building loads are distributed in the concrete at an angle of 45°. The concrete strip foundations in Figure 8.3 are Width of the foundation related to the type of soil Figure 8.3 A concrete strip foundation for a load-bearing wall. Foundations 43 Deep strip foundations The deep strip foundation in Figure 8.4 is a varia¬ tion of strip foundations. Deep strip foundations are usually dug out with a mechanical excavator, which cuts a narrow trench that is backfilled with concrete up to ground level. These foundations use more concrete, but reduce the cost of masonry walls and may remove the need for timber support for the trenches. Raft foundations Figure 8.4 Deep strip foundation. Raft foundations are a good solution if the soil has a poor bearing capacity or if the building loads are quite small, because the cost of digging separate foundations is eliminated. The oversite concrete slab that forms the ground floor of the building becomes the raft foundation (Figure 8.5). The slab can be thickened at the edges with an edge beam and thickened underneath internal load-bearing walls. Mesh reinforcement increases the strength of the raft foundation and distributes the pressures of the building loads evenly. See Chapter 11 for more information about the con¬ struction of raft foundations. Loads are distributed by the slab A larger area of ground supports the loads Figure 8.5 Raft foundation. 44 Building construction Pad foundations Pad foundations are isolated foundations that sup¬ port concrete columns or free-standing brick piers. A square concrete pad foundation distributes the load evenly over the ground. If the pad is constructed of mass concrete, then the thickness must equal the projection from the side of the column. You can see this in Figure 8.6. The size of the pad foundation depends on the total building loads and the load-bearing capacity of the soil. Chapter 22 has more information about the construction of pad foundations. Stepped foundations i l Figure 8.6 Pad foundation. Figure 8.7 Stepped foundation. Stepped foundations are built on sloping sites (Figure 8.7). This reduces the expense of con¬ structing a foundation that is the same level around the perimeter of the building. A foundation at the higher end of the slope would be extremely deep. To overcome this, you can step the foundations at different levels. The higher-level foundation should extend over and meet with the lower one for a distance not less than its thickness. This should never be less than 300 mm. The change in level should not be more than the thickness of the strip foundation. It should be measured in multiples of 75 mm, which is the height of a brick course. 45 Foundations Piled foundations If soil conditions are poor near the surface, then you should use piled foundations. Trial holes will usually indicate the depth of suitable load-bearing soil. Since this may be as deep as 2 or 3 metres below ground, it would be quite expensive to construct conventional foundations. You can use two types of piled foundation to strengthen the soil and overcome this problem: 1. bored or replacement piles, which are con¬ crete cores poured into holes in the ground at ■ measured intervals; 2. driven or displacement piles, which are tree trunks that are hammered into soft ground at spaced intervals. Short-bored piled foundations Short-bored piled foundations are used for small houses and lightweight framed buildings constructed on soils that expand and contract with changes in Load-bearing wall Reinforced concrete raft the moisture content. These soil types include clay and black cotton. You can construct the type of foundation shown in Figure 8.8 quite quickly and avoid the need to dig deep trenches. Short-bored piles are more ef¬ fective and cheaper than conventional foundations if the soil responds easily to the changes in the atmosphere. These foundations are not suitable for use on rock, flint or sites with many tree roots because the holes must be straight and consistent in diameter. You dig the holes by hand with an auger and then pour concrete in them to form a column in the ground when it hardens. The concrete columns in the holes in the ground are the piles. Typically, piles would be about 1200 mm apart so that they spread the load evenly. They should be placed on the centre line of the walls that need support. The piles can support the walls because you then form lightweight beams at ground level, re¬ inforced with two bars. Where a beam crosses a pile, the reinforcement should extend to each side of the pile for a quarter of the distance between adjacent piles. This takes the pressure from the building loads. The measurements in Table 8.2 are typical dimensions for short-bored piles. Table 8.2 Measurements for short-bored piles Measurements (mm) Components Depth of the hole for the piles 2500-3000 Pile diameter 250-360 Pile spacing 1200 Beam width for 225 mm wall 300 Beam depth for 225 mm wall 150-200 Reinforcement diameter 15 mm with 6 mm stirrups Timber displacement piles Figure 8.8 Short-bored pile foundation. You use suitable lengths of straight tree trunks to make timber displacement piles for lightweight buildings as you see in Figure 8.9- They should be treated with preservative and sharpened at the ends to drive them into the ground. It is better to use an auger to remove some soil before you start the pile-driving process. You should leave the piles sticking out above ground so they can support timber beams for timber flooring. 46 Building construction Table 8.3 Calculating the size of strip foundations Step 1 Action Find the area of the foundation: . Load (in kN) Area (in m2) = -—:-—, ... Bearing capacity (in kN/m2) For one metre length: .., ,,, Load Width = —-:-:— Bearing capacity Example: Width = = 0.347 = 347 mm (say 350) 2 Find the width of the foundation projections: Foundation width (mm) - wall thickness (mm) 2 Example: 350 - 215 ___ -= 67.5 mm 2 3 driven piles Find depth of foundation: Depth = projection, but depth must be at least 150 mm Example: Projection = 67.5 mm Depth must be 150 mm Figure 8.9 Timber displacement piles. 4 Result: Foundation size = 350 x 150 mm Designing strip foundations The calculations for a strip foundation depend on the load-bearing capacity of the soil and the pres¬ sure of the load to be supported. The formula for this is: Area of foundation = Load/bearing capacity. The thickness of the foundation must be at least 150 mm. Table 8.4 Calculating the size of pad foundations Step 1 Find the area of the foundation: Area of the foundation = load/bearing capacity Example: Area - 11.52/65 = 0.177 m2 In the example in Table 8.3 for a single-storey house Bearing capacity of ground = 72 kN/m2 Wall thickness =215 mm Load on foundations = 25 kN/m Action 2 Find the size of the foundation: For a square foundation the length of each side is the square root of the area. Example: Trn = 0.42 - 420 mm 3 1 kg is equivalent to 9-81 newtons 1 kilonewton = 1000 newtons For rough calculations, you can assume that 1 kg is equivalent to 10 newtons Find the depth of the foundation: Depth = projection Minimum depth must be at least 150 mm. V Example: 420- 215 = 205 mm 205/2 = 102.5 mm Minimum depth = 150 mm 47 Foundations Designing pad foundations You will need some data to design pad founda¬ tions for piers or columns. Table 8.4 describes how to calculate the size of pad foundations using information about the loading pressure of various parts of the building. In the example in Table 8.4 for a pad foundation the calculations use the following sample loading pressures: Roof 6 kN Brick pier 3.36 kN Concrete base 2.16 kN Total building load = 11.52 kN Bearing capacity Pier size = 65 kN = 215 x 215 mm 3 4 5 6 Describe the purpose of a raft foundation. What factors control the width and thickness of a strip foundation? Draw a section of an outer wall of a two-storey building on a strip foundation and show the different building loads. Compare the costs of forming a strip founda¬ tion with a deep strip foundation as shown in the drawings in Figure 8.10. Costs should be in your own currency where * is shown. Concrete = *650 per metre run at 250 mm thick Brickwork = *1000 per metre run in the foun¬ dation Backfill = *200 per metre run of trench. CHECK YOUR UNDERSTANDING The natural foundation is the ground under¬ neath the artificial foundation. • Artificial foundations ensure the stability of the building. Load-bearing walls require strip or deep strip foundations. Columns and piers require pad foundations. Light loads or poor soil conditions require raft foundations. • Very poor soil conditions such as clay and sand require piled foundations. • The size of a foundation is determined by the pressure of the load and the strength of the soil. • Stepped foundations are used on sloping sites to reduce costs. • Piles can be: replacement piles that are con¬ crete-filled holes; displacement piles that are tim¬ bers driven into the ground. 600 Concrete strip foundation REVISION EXERCISES AND QUESTIONS 1 2 Convert 1250 kg to kilonewtons. Calculate the size of a pad foundation for a point load of 31 250 kg on a soil bearing capacity of 52 kN/m1 2. Figure 8.10 Question 6. Dimensions for two types of strip foundation. Walls Introduction Walls separate the spaces inside and outside a building. This chapter describes different types of wall and their construction, which is called ma¬ sonry in this book. Because brick and blockwork walls are so im¬ portant, the basic techniques for building these types of wall are also described. Load-bearing external walls (Figure 9.1) These walls are normally used for domestic build¬ ings or other small structures that are one or two storeys high. The weight of the roof and any upper floors is supported by load-bearing masonry of brick, block or stone construction. Types of wall Non-load-bearing external walls (Figure 9 2) These walls are often built from corrugated sheet cladding that is attached to a framework of timber or steel rails and columns. The cladding sheets do not support the structure of the building. Support is provided by the framework. The cladding sheets must be wind-resistant. This section describes the different types of wall commonly found in small buildings. Walls can be divided into the following types. Load-bearing internal walls (Figure 9 3) Internal walls are load-bearing if additional sup¬ port is needed for the roof or floors. These walls A roof truss Figure 9.1 Load-bearing external walls. 48 Figure 9.2 Non-load-bearing external walls. 49 Walls will need to be strong and stable. They usually stand on a concrete foundation. Non-load-bearing internal walls (Figure 9 3) 8. good construction and use of materials. Internal walls should have these characteris¬ tics: Characteristics of walls 1. positions that provide separation between rooms; 2. sound insulation that provides a reasonable level of noise control between adjoining rooms; 3. stability to resist normal impact and to support fixtures and fittings; 4. fire-resistance to prevent the rapid spread of fire to adjoining rooms. This section describes the main characteristics of external and internal walls. External walls should have these characteris¬ tics: Building materials for external walls These walls divide the internal space in buildings and stand independently of the main structure. The majority of internal walls are in this category. 1. strength to resist being crushed by the loads from floors and roofs; 2. stability to resist other forces such as wind pres¬ sure and roof loads; 3. weather resistance to keep out wind and rain; 4. thermal properties to keep the interior cool in hot weather and retain warmth in cool weather; 5. durability; 6. fire-resistance to provide security and stability in the event of fire; 7. openings for daylight and ventilation; Some construction methods use locally available materials and techniques that are economical and ecologically sound. Many different types of ma¬ terial are available, but the two main requirements for building materials are stability and durability. The three most common materials for external walls are: • natural stone; • bricks; • cement-based blocks. 50 Building construction Natural stone masonry uses stone that is re¬ moved from the ground and broken and shaped into suitable-sized pieces for building. You can use most stones, but you need to check for durability. This is an economic building material since the stone is often freely available. The cost is in the manual work to quarry and shape it. Bricks are made from clay that is found in the ground. You dig out the clay and mix it with water to make a pliable material that you can mould into a specific shape. Using moulds ensures that the bricks are a consistent size. When the moulded bricks dry out they are fired in a kiln. This process transforms the clay into a hard, strong material. The main costs of brick production are the manual work required to mould the bricks and the fuel to fire them. Cement-based blocks are manufactured from a mixture of ingredients. The cement binds the ag¬ gregate that forms the bulk of the block into a firm building material. The strength and durability of the block depends on the type of aggregate used with the cement. Blocks consist of natural materials that are moulded and cured such as: standard brick is 215 x 102.5 x 65 mm, but the bricklaying unit is 225 x 112.5 x 75 mm. The dimensions of standard blocks are related to a brick face which measures 215 x 65 mm. This means that a block length is equal to two bricks plus a 10 mm joint: 440 mm. The height of a block equals three bricks plus two joints of 10 mm, or 215 mm. Table 9.7 Masonry dimensions Masonry material Minimum size (mm) Maximum size (mm) Natural stone 75 x 100 x 300 300 x 200 x 200 Bricks 65 x 102.5x 215 70 x 115 x 240 Concrete blocks 50 x215 x440 215 x 215 x 440 Sandcrete blocks 150 x 230 x 460 Variable Landcrete blocks 140x220 x 290 Variable Mortar 1. sand (sandcrete). You mix sand with cement in 1:4 or 1:6 proportions; 2. stone (concrete). The strongest blocks are made from a mixture of cement, sand and crushed stone. A third type of block, called landcrete, is made with earth. This type of block is usually not suit¬ able for external construction. You can make blocks that are solid or have holes in them. Those with holes, called hollow blocks, weigh less and are weaker than solid blocks. They are most suitable for non-load-bearing inter¬ nal walls. The composition of cement-based blocks is described more fully in Chapter 21. Dimensions Masonry materials need to be a convenient size and weight for a person to handle since external walls are built by hand. The three main types of building materials have fairly standard dimensions, although they may vary slightly from country to country. You can see examples in Figure 9.4. The standard dimensions for bricks include an allowance for a 10 mm joint on each edge, which adds 10 mm to measurements. For example, a Masonry walls also need mortar. Mortar is the mixture of cement, lime and sand that is used to join the individual units of the building material into a uniform mass. The purpose of mortar is to provide: • a level bed for the brick, block or stone to sit on to maintain horizontal and vertical stability; • a water-resistant filler between the units to pre¬ vent the penetration of water into the interior of the building. Mortar mixes of cement, lime and sand are combined in a range of mixes, depending on the application. Cement and sand mixed in proportions of 1:3 give greater strength. Flowever, the addition of lime: makes it easier to spread the mortar; reduces shrinkage; lengthens the time that the mortar is still pliable. The mortar should be weaker than the ma¬ sonry so that any movement will crack the mortar instead of the wall. It is easier to re¬ pair cracked joints than to repair cracked masonry. Walls 51 (a) Figure 9.4 Examples of the standard dimensions of masonry materials: (a) standard block dimensions; (b) standard brick dimensions. 52 Building construction Forming joints with masonry The mortar joint affects the appearance of the finished wall. You can see from Figure 9.5 that you can form four types of joint for different results. The flush joint is a joint where the mortar joint is level with the masonry. This gives a flat appear¬ ance. The weather-struck joint is a joint where the mortar is levelled off with a trowel at an angle that slopes down and out. This enables rain to run off an external wall more easily. The half-round joint is a semicircular concave joint that is formed with a steel rod drawn along the joint. This is an easier joint to make than the weather-struck joint and performs the same func¬ tion. The recessed joint is a vertical joint that is set back 4 to 5 mm. This joint is formed with a square rod. You should finish the work on the joints by brushing off dry, surplus mortar with a wire brush. When the joints are completed, then you should leave the masonry for a couple of days before you do any more work on the external walls. Technical words used in bricklaying It takes time to acquire bricklaying skills and fa¬ miliarity with the tools and techniques. There are also many specialist words that are used in brick¬ laying. This list defines the main words that you will need to know: Arris the edge of a brick. Bat a brick that is cut across its width. Bed the bottom of the brick when it is laid in a course. Bed joint the horizontal mortar joint. Brick gauge a wooden batten with the courses marked on it (usually four courses for a height of 300 mm). Closer a brick cut in half along its length. Course a complete layer of bricks including the mortar. Face a header or stretcher surface that is exposed in the work. Lap the horizontal distance that one brick over¬ laps the one below it. Quoin a corner or external angle. Perpend a vertical continuation of the vertical Figure 9.5 Examples of mortar joints. joints. It should be straight. Racking back the stepping back of the brick¬ work so that a wall does not rise more than 900 mm above the adjoining work. This avoids uneven settlement. 53 Walls V rrrm If the bricks have straight vertical joints, then they are not bonded If the bricks overlap to avoid continuous vertical joints, then they are bonded Figure 9.6 A comparison between bonded and non-bonded brickwork. Bonding two separate skins of brickwork beside each other. You use wall ties to tie them together. Bonding is the method used in masonry work to avoid continuous vertical joints, which can make a wall unstable when loads are uneven. A complex bond produces a stiffer wall. Bonding also spreads the loads from joist ends and roof trusses through the wall. Header bond You make this bond on a 215 mm wall by laying the bricks lengthwise across the wall. This results in a simple pattern with the brick ends (or headers) visible. Bonding in brickwork A brick should be twice as long as it is wide. This allows for different methods for bonding the bricks, which can produce variations in appearance and strength. Figure 9-6 shows you a comparison be¬ tween bonded and non-bonded brickwork. This section describes some of the common types of bond used in small building works. Stretcher bond You can use this bond if an internal load-bearing wall or the external skin of a cavity wall is the width of a single brick (about 102.5 mm). One brick course overlaps another by half its length to make a regular, simple pattern. If you prefer the appearance of stretcher bond for walls that are 215 mm thick, then you can bond English bond You combine the header and stretcher bonds in the method shown in Figure 9-7. Lay the first course with two rows of stretcher bonds without using wall ties. The next course consists of all headers that you lay across the stretchers. One header should lie over the centre of each stretcher and over each joint between the headers. This produces a more interesting pattern and very wellbonded construction. Notes on English bond (Figure 9 7) Place alternate headers and stretchers in the same course. Join the closer brick with the corner header. Place each header centrally over a stretcher. • Line up perpends vertically. 54 Building construction Flemish bond You use both headers and stretchers in brickwork courses in this order: # a header; • two stretchers side by side; a header, and so on. This order is repeated in each course of brick¬ work so that the header is located above the centre of the stretchers below. Figure 9-8 shows you how the pattern should look. cut the bricks in half along their length and build them into the wall a half-brick length from the corner or quoin. This cut brick is called a closer (Figure 9.8). You can use closers in English and Flemish bonds. Bonding in stonework Bonding in stone is more random because the blocks may not have a regular shape or size. To increase stability and to spread loads, you should avoid continuous vertical joints and take some of the blocks right through the wall. Openings and corners Bonding in blockwork If you have to stop the brickwork at door and window openings or to change direction at cor¬ ners, then you must ensure that the bond remains strong and that the appearance is good. You can Concrete and cement blocks are the cheapest form of blocks for walls and they are rarely chosen for their appearance. The only type of bond that you Opening for the door or window Brick pier bonded into the wall Closer Brick quoin Figure 9.7 Wall construction in English bond. 55 Walls Alternate headers and stretchers in each course Brick pier bonded into the wall Brick quoin Closer Figure 9.8 Wall construction in Flemish bond. can use is the stretcher bond. This means that you should place each block centrally over the joint of the one below so that you avoid con¬ tinuous vertical joints. Bricklaying tools and equipment Bricklaying uses these materials: cement in bags; a supply of sand; hydrated lime in bags; water. In addition, you may need to use scaffolding as the work rises up the building. You will need these bricklaying tools and equip¬ ment for your work: shovel for mixing mortar; pointing trowel; bricklayer’s trowel; mortar board; spirit level; metal pegs and line; mixing board; • handbrush and a bowl of water. How to build a brick wall Building a successful brick wall is one of the most important skills needed on a building site. Table 9.2 describes the procedure step by step. Figures 9.9 and 9-10 describe how to mark the positions to align the bricks correctly using a builder’s level or a plumb-line. 56 Building construction Table 9.2 Building a brick wall Step Action 1 Use the profile lines to locate an external corner on the strip foundations. 2 Use a builder's level held vertically or a plumbline to mark the position of the external corner with wet mortar. Repeat steps 1 and 2 for all four corners. 3 Stretch a line between the corners to provide a position for the first course of bricks. Secure the line by wrapping it around a brick and putting another brick on top. Remove the line after the first course of bricks is laid. 4 Lay the bricks in a row. Adjust their position by tapping the bricks with a trowel. Check that they are level horizontally and vertically with the builder's level. 5 Build up the corners by racking the bricks back for 8 or 10 courses. Check your accuracy with the builder's level. Use a gauge rod to control the height. 6 Insert metal pegs in the mortar joints on the corners for each completed course of brickwork. Stretch a line between the pegs so that it is flush with the surface of the brickwork to provide a guide for the next course of brickwork. 7 Continue checking horizontal and vertical levels. 8 Form the joints while the mortar is soft. Using a damp-proof course with brickwork below ground Construction below ground is vulnerable to damp¬ ness from the water that soaks into the ground. A damp-proof course (dpc) prevents the dampness from rising into the interior of the building. It is a waterproof barrier that separates the brickwork below ground from the brickwork above. The dpc is a bitumen-based felt material wide enough to cover the width of a wall. It is rolled out on a brick wall that is 150 mm above the ground and laid in a mortar bed. If joints occur, then they should be lapped at least 150 mm. The height above the ground prevents heavy rain water splash¬ ing the wall and bypassing the dpc. A concrete floor slab will have a damp-proof membrane (dpm), which is a layer of moistureproof material laid under a concrete slab and screed to prevent rising damp in floors. If the dpm meets the dpc, then they should be lapped to provide continuity of the resisting barrier (Figure 9.11). Pier construction A pier is a column of brickwork that may be free¬ standing or attached to a wall to provide extra strength or stability. You can use either English or Flemish bonds in pier construction. The choice depends on the size of the pier. Figure 9.9 Setting out a corner of a brick wall using a plumb-line. Walls Figure 9.10 Laying the first bricks in a brick wall. Figure 9.11 Detail of the overlap between a dpc and a dpm. 57 58 Building construction A roof truss supported by a pier Lintel A pier strengthens and stiffens a jamb Figure 9.72 Piers attached to a wall. A pier attached to a wall as in Figure 9.12 can stiffen it, which makes it stronger and more resist¬ ant to forces such as wind pressure. You can also build a pier in a wall where a point load from a roof truss creates an extra load-bearing pressure. Piers strengthen the openings in the walls and help to support the loads from the lintels or arches that span openings. Free-standing piers usually support point loads from beams, lintels and trusses. For stability, there is a specific ratio called the ‘slenderness’ ratio between the pier’s height and width. An 8:1 ratio is the standard limit for height and width. If a pier is too narrow then it will buckle. If a brick pier is 215 x 215 mm wide, then it must not be taller than: Column construction Reinforced concrete columns are not usually put in small buildings. If they are used, then the rein¬ forcement in the column must be tied into the reinforcement of the beam or slab. Setting out columns is described in more detail in Chapter 6. The sides of the formwork can be timber planks fixed to timber members called yokes at 300 mm centres. You bolt the yokes together and tension them with wedges to make sure that no loss of liquid occurs when the column is poured. You should use a plumb-line to check that the column is vertical. After the concrete is poured, you can usually remove the formwork two days later. The height of the column is determined from the drawings. 8 x 215 mm = 1720 mm If a pier is 3000 mm high, then its width must be at least: Since the closest brick dimension is 440 mm, then a square pier would be: 3000 x 440 x 440 mm Openings in brick walls Doors and windows are the main openings in brick walls. Their location is shown on the work¬ ing drawings together with the cill and head heights. These heights should relate to the datum or oversite slab level. If this is not the case, then you must recalculate the heights and decide which brick courses will take the openings. 59 Walls Finish off the brickwork neatly on each side of the opening with a stop-end. The method is simi¬ lar to finishing off at a quoin. Insert a closer before the last header in alternate courses in English and Flemish bond. The cill does not need special treatment, but at the head there are alternative methods to carry the brickwork across the opening: ® lintels; # arches. Table 9.3 Standard dimensions for lintels Span Depth Reinforcement bar diameter 900 mm 150 mm 10 mm 1200 mm 150 mm 12 mm 1500 mm 215 mm 12 mm 1800 mm 215 mm 16 mm The design of the lintel should use these addi¬ tional measurements: Lintels A lintel (Figure 9-13) is a beam that spans across a horizontal opening and supports the load just above the opening. Lintels can be timber or concrete. Timber is fine for short spans, but is not durable. For this reason, most lintels are built from rein¬ forced concrete. The lintel can be covered with a skin of decora¬ tive brickwork, which needs support. This is done by: 1. bolting a galvanised steel angle to the concrete lintel; 2. building the decorative brickwork on the edge of the angle; 3. tying the brick joints to the lintel with metal ties. Constructing concrete lintels Structural engineers design lintels for larger build¬ ings, but you can follow these basic guidelines to construct a lintel for domestic-scale construction. Tables 9.3 and 9.4 define the standard measure¬ ments for smaller lintels. Figure 9-13 illustrates the different parts of lintel construction. 1. one reinforcement bar for each 112 mm width of lintel; 2. the width must be at least l/20th of the span; 3. the bearing of the lintel must be more than 150 mm; 4. at least 25 mm of concrete must cover the bottom of the reinforcement bar; 5. at least 50 mm of concrete must cover the ends of the bar. The ends of the reinforcement bars should have L-shaped hooks to spread the load cor¬ rectly when they tie into a slab. Casting a concrete lintel After designing the lintel, it should be cast (or made). Lintels can be cast in situ or precast. The span will determine the height of the lintel, which should correspond to the height of full brick courses. Example 2 bricks + 1 joint = 140 mm lintel 3 bricks + 2 joints = 215 mm lintel 4 bricks + 3 joints = 290 mm lintel Table 9.4 Weights of typical concrete lintels (concrete density 2400 kg/m3) Length = span + 2 x bearing (mm) Volume = length x width x depth (m3) Weight (volume x density) 900 + 300 = 1200 1.2 x 0.215 x 0.150 = 0.0387 0.0387 x 2400 = 1500 + 300 = 1800 1.8 x 0.112 x 0.215 = 0.0433 0.0433 x 2400 = 104 kg 1800 + 360 = 2160 2.16 x 0.19 x 0.215 = 0.0882 0.0882 x 2400 = 212 kg 93 kg 60 Building construction (a) :=- Figure 9.13 Forming a concrete lintel: (a) a lintel spanning an opening; (b) a lintel in situ; (c) making the steel reinforcement for the lintel; (d) precasting a reinforced concrete lintel; (e) using concrete spacers to raise the steelwork. r//IIII (c) 61 Walls Precasting is the process of making the lintel separately from a building. It can be done on or off site. The advantage is that the lintel can be placed in position as soon as the brickwork is ready. If the lintel is heavy, then you will need to lift it into position with mechanical equipment. Table 9.5 Making a precast lintel Step Action 1 Make a timber box with an open top, which is the same size as the external dimensions of the finished lintel. 2 Paint the inside of the box with a releasing oil. This stops the concrete sticking to the timber. 3 Bend the ends of the reinforcement bars to right angles (90°). If the lintel contains more than one bar, then make short cross bars and wire the cross bars to the long bars. 4 5 Insert spacers that hold the bars 25 mm from the bottom of the formwork. Spacers are small cement blocks embedded with tie wires that you use to attach them to the bars. Place the reinforcement bars in the formwork and check that the bars are 50 mm from each end of the box and supported by spacers. 6 Mix the required amount of concrete. 7 Pour the concrete into the timber box and make sure that it flows down around and under the rods, then pack it down to remove any trapped air. 8 Make a smooth finish on the top of the concrete with a wood float and write the word Top on the wet concrete. 9 Cover the box with wet sacking and leave to set for seven days. Precast lintels are often better quality, but you must remember to mark the top of the lintel very clearly to make sure that it is put in the right way up. 2. Place the reinforcement. 3. Pour in the concrete. After the concrete hardens, you remove the formwork. This method increases the labour ele¬ ment of the job and may slow down the brick¬ laying. You can cut the facing bricks in half to widen the lintel and increase its strength. You can also cast a lintel so that the bricks are supported by a ‘toe’. This means that a strip of concrete is visible at the head of the window. Table 9.6 Making an in situ concrete lintel Step Action 1 Erect the timber formwork across the opening and support it from the floor below. Use wedges to level the supports and formwork. 2 Seal all the joints with building paper or mastic between the timber formwork and the brickwork to stop the cement and water leaking out. 3 Paint the inside of the formwork with releasing oil. 4 Place the reinforcement in the formwork using the same method described in Table 9.5. 5 Pour the concrete as described in Table 9.5 and cover it with wet sacking and leave for seven days. Beams If an opening is very large, then the walls may not give enough support to a floor or roof. In these cases, you would normally put in a steel or rein¬ forced concrete beam as part of a reinforced con¬ crete floor slab. You might also use a tie beam at the top of an external wall that encloses the four sides of a building. This improves the stability at the top of the wall where the roof is tied down to the brick or blockwork. A beam has anchors to secure the wall plate as you can see in Figure 9-14. Arches Casting in situ is the process of pouring the concrete into the formwork across the opening to make the lintel. When the brickwork is ready: 1. Put the timber formwork across the opening. You can make arches from bricks or stones to span openings and support the structure above them (Figure 9.15). An arch depends upon the tension in 62 Building construction Anchors cast in the ring beam Wallplate Ring beam Figure 9.14 A beam secured to a wall plate by steel anchors. the structure for its stability. The downward pres¬ sure forces the units of the arch together and in¬ creases their resistance as long as the load does not exceed the strength of the arch building material. The advantages of segmental and semicircular arches are: 1. They avoid the need for concrete and steel. 2. They use local stone or bricks. 3. Their appearance is pleasing in many stone or brick buildings. The disadvantages of these arches are: 1. Doors and windows will need timber frames to fit the curve snugly. 2. The timber centrepieces or turning pieces must be made accurately. 3. Arches must be formed in situ. Technical words for parts of arches Arches have many technical words to describe the parts of their structures. Figure 9.15 A semicircular arch in sandstone. Walls Abutment the point where the ends of the arch rest on the wall and support the weight of the structure above them. Centre the centre of the circle that defines the segmental arch. Crown the highest point of the extrados. Depth the distance between the intrados and extrados. Extrados the upper surface of an arch. Haunch the lower part of the arch between the crown and the skewback. Intrados the undersurface or soffit of the arch. Keystone the central stone or brick at the top of the arch, which may be wedge-shaped. It holds the arch together. Radius the measurement used to define the cen¬ tre of the arch and the curve of the intrados. Rise the vertical distance between the springing line and the highest point of the intrados. Skewback the splayed surface of the abutment which receives the arch springer. Span the horizontal distance between the spring¬ ing points. Springer the first stone or brick laid on the skewback. Springing line the line that joins the springing points. Springing point the point where the intrados meets the skewback. Making a brick arch Semicircular and segmental arches are the easiest to build with normal square bricks. The designer Figure 9.76 Different types of arch. 63 should show the rise of a segmental arch on the working drawings. The span of the opening deter¬ mines the rise of the semicircular arch. Figure 9.16 shows you what the different types of arch look like. The stages of construction of an arch are shown in Figure 9.17. Centring an arch An arch must curve upwards to be self-supporting. To achieve this you need to make a timber shape with the same curvature as the completed arch. This timber shape is called the centring or turn¬ ing piece. It can be made from a single piece of timber that is shaped to the curve or two timber ribs spanned by battens to maintain the width of the arch. A semicircular arch needs additional struts and braces to support the ribs The centring must be strong enough to support the weight on the masonry until the cement mortar is hard. It is supported on vertical props. Wedges inserted between the top of the props and the centring allow you to adjust the level and width of the arch. Timber framework should support the centring in the exact position where you plan to form the arch. Place the bricks or stones for the arch one at a time and cement them together. You may want to move the centre slightly while the mortar is soft so that the bricks can settle against one another in a firm wedge. The arch or its joints may crack if there is no movement before the mortar sets. When the cement is hard, then you can completely re¬ move the centring. 64 Building construction (d) Figure 9.17 The stages of building an arch: (a) constructing the centring; (b) spanning the arch; (c) placing the centring in position; (d) building the arch out of bricks-on-edge; (e) placing the key brick. 65 Walls An alternative is to position a door or window frame in the opening. Using a curved member on the top of the door or window frame, you can make an arch on top of the frame. Cavity walls The normal 215 mm solid wall does not keep out moisture if there is considerable rainfall or cold weather. The solution is to build cavity walls, which are walls built in two separate layers with a space of 50 mm between them (Figure 9.18). The outer layer can be wet while the inner layer re¬ mains dry. The 50 mm space is a cavity that acts as a moisture barrier and improves the insulation of the inner wall. In cold weather, the heat does not escape so easily so the interior of the building is drier and warmer. In hot weather this is reversed and the interior stays cool longer. Wall ties attach the internal and external layers, called skins, of the walls together. This ensures that cavity walls have the same strength and stabil¬ ity as solid walls. The wall ties are galvanised metal or plastic. They are placed in staggered patterns 450 mm apart vertically and 900 mm apart horizon¬ tally. A vertical damp-proof course at the jambs of openings and lintels prevents dampness in the inner layer (Figure 9-19). If mortar falls down the cavity and lodges on the wall ties it can form a bridge from the external to internal skins. The result is damp patches on the internal wall. To prevent this, you can suspend a batten in the cavity to collect falling mortar. From time to time during construction you should take out the batten and clear away the debris. Moisture that collects in the cavity must escape. You can help this process by leaving out some vertical mortar joints at ground level in the external skin. Since insects can enter the cavity through these open joints you should cover them with mesh. The reinforced concrete floor is supported on the inner leaf '°y Inner leaf Outer leaf Cavity — Stepped flashing ••‘it m Dpc under the cill ]C 50 mm Dpc The cavity is filled below ground to resist pressure Stone walls Stone is the hard material that forms the earth’s crust as well as the mountains in the landscape. You can break up and use three types of stone for building: Figure 9.18 Cavity wall construction. 66 Building construction Figure 9.19 Details that prevent the entry of moisture into a cavity wall. # igneous rock; # sedimentary rock; # metamorphic rock. Igneous rock is the oldest type of rock. Formed from molten material in the earth, these rocks are usually very hard. Granite is a typical example. Sedimentary rock consists of particles of igne¬ ous rock that are carried by water and hardened under pressure to form new rocks. Limestone and sandstone are common sedimentary rocks. A third type of rock is metamorphic rock. Changes in igneous and sedimentary rocks under heat and pressure create this rock. Marble is a metamorphic rock that is formed by changes in limestone. Rock should be quarried and broken down into stone pieces that can be worked into suitable shapes for building work. Shaping the stones is called dressing. The use of the stone depends on the amount of dressing done to it. Building a stone wall The stonemason needs to be skilled to select and dress each stone for a wall. If the stones are irregular, you can fill the spaces in the middle with smaller pieces to save mortar. Some stones must be long enough to bond the front and back of a wall properly. These stones are the header or bonding stones. Bonding at the corners is important. You can use large stones to overlap each other in alternate courses to avoid producing straight vertical joints. Types of stone wall There are four types of stone wall. Uncoursed random rubble walls (Figure 9.20) consist of rough stones used in an almost natural state. You may do a little dressing to remove awkward projections. The pieces are not a consis¬ tent size, so it is up to the experienced mason to build a wall that is stable and pleasing to look at. The basic rules of wall construction are the same: You need many of the same tools for stone ma¬ sonry as for bricklaying. Stone masonry does use some special tools as well, for dressing and shap¬ ing irregular stones: 1. avoid continuous vertical joints; 2. use enough stones to reach from surface to surface to provide a crosswise bond. Each square metre of wall should have two or three header stones. 1. the mason’s hammer which is flat at one end and sharp at the other. You use it to break or chip stones; 2. the chisel or punch that you use with a hammer to dress the face of the stones; 3. the pitcher that you use to cut stones to a fair surface. It has a wider cutting edge than a chisel. Coursed random rubble walls (Figure 9.21) are made of stones that are squared off with a hammer to make them more regular. You lay coursed rubble randomly, but form a level vertical course about every 300 mm. Squared rubble walls built to courses (Fig¬ ure 9-22) consist of stones that are dressed with a 67 Walls Figure 9.20 An uncoursed random rubble stone wall. Level course Figure 9.21 A coursed random rubble stone wall. Figure 9.22 A squared rubble wall built to courses. Figure 9.23 A regular coursed rubble stone wall. 68 Building construction cold chisel and hammer to produce accurate shapes. You lay squared rubble in courses, although a large header stone may interrupt the line. The courses may be short. Regular coursed rubble walls (Figure 9-23) are stones of the same height laid in continuous courses. You need skill, experience and the right tools to dress these stones correctly. The height of the stones in one course may differ from the height of the stones in the next. Checklist for building with stone Rocks have a natural bed on the horizontal surface. You should lay rocks so that the bed remains horizontal. Overlap the stones to avoid continuous vertical joints through the courses. Include header stones that go through from the external to internal surface. Use small pieces of stone to prop up larger stones when you build in random rubble. Use small pieces of stone to pack spaces between larger stones to save mortar. Use large stones to form the corners and the jambs of openings. Figure 9.25 Examples of masonry blocks. V Block walls Blocks can be used for: internal and external walls; load-bearing and non-load-bearing walls; solid and cavity walls. Figure 9.24 The insertion of a closer in bonded blockwork. Blocks are laid in level courses in stretcher bond formation. You need to cut the blocks to make closures at the junctions, openings and corners to maintain true stretcher bonding (Figure 9.24). The joints can be raked out to provide an additional hold for plaster or render. Concrete lintels should span the openings in block walls, since it is not easy to form arches using concrete blocks unless they are made for the purpose. 69 Walls Many statutory authorities issue quality stand¬ ards for manufactured blocks. The factory-produced blocks can be made in controlled conditions and tested for strength and density. Where standardised blockmaking doesn’t exist, you will need to follow the general principles of block manufacture. 1. 2. 3. . 4. 3. 6. Blocks should be a uniform shape and size. They should relate to the standard brick sizes for convenient bonding. The minimum crushing strength of the weakest block must not be less than 2.8 N/mm2. Blocks should be available in a range of strengths to suit a variety of purposes. The source of the aggregates used in the pro¬ duction of the blocks should be known and it should be covered by quality standards. The type of blocks in Figure 9-25 should be available: A) solid blocks with no formed holes or cavi¬ ties; B) hollow blocks with one or more holes or cavities. Blocks should consist of a mixture of some of these materials: A) cement; B) sand; C) lime; D) natural aggregates; E) laterite soils; F) pulverised fuel ash from power stations; G) blast furnace clinker from steel works; H) wood chips and shavings from sawmills. Choosing the right type of block The type of block you use depends on: 1. the purpose; . 2. the amount of exposure to the weather; 3. whether or not external treatments such as render will be applied; 4. the load on the blockwork from internal struc¬ tures such as floors and roofs; 5. the weight of the finished partition; 6. the degree of sound or thermal insulation required. Block weights Different types of block have fairly standard weights. These weights are shown in Table 9-7. Table 9.7 Block weights Type of 100 mm block Weight (kg) Solid blocks with natural aggregates 21 Hollow blocks with natural aggregates 13 Solid blocks with natural aggregates 11.5 Hollow blocks with natural aggregates 9.5 Making concrete blocks on site Blocks made on site will be cement with laterite soil or sand as the usual aggregate. The strength of the block depends on the strength of the aggre¬ gate. The cement is the binding agent. The in¬ gredients should be combined in a concrete mixer to ensure an even mix and to produce enough material. If sand is the aggregate, then the blocks should consist of 1 part cement to 6 parts sand. You should add just enough water to dampen or hydrate the cement. When you succeed in adding the right amount of water you should write down the specific proportions of cement, sand and water. These blocks are strong enough for loadbearing walls in two-storey buildings. You should not be able to press out any water when you squeeze a handful of concrete mix. If you use laterite soil as the aggregate, then the landcrete blocks will be suitable for non-load¬ bearing walls. External walls made with landcrete should be rendered to keep out the moisture. The ratio of cement to laterite is about 1:8. Again, the water should be added carefully so that the mixture is not runny or dripping wet. Making blocks on site has these disadvantages: 1. you need to supervise the process closely to ensure quality; 2. the process takes about 28 days to produce usable blocks; 3. the process requires considerable space for production and storage. Like other cement-based products, the blocks must be cured by keeping them covered with wet sacks for about seven days. 70 Building construction sheet or timber cladding is classified as non-load¬ bearing. Iron sheets must be supported on a framework with columns that transfer the building loads and wind pressure from the structure to the foundation. The columns transfer point loads to the founda¬ tion, unlike the evenly distributed loads transferred by the load-bearing wall to strip foundations. Chap¬ ter 24 has more information about building loads. Corrugated iron sheets have disadvantages as a building material for external walls for housing: Figure 9.26 Building a timber mould for blockmaking. Using timber moulds for block making The mould that you can see in Figure 9.26 consists of: 1. four pieces of timber that form the shape of the block; 2. wedges to hold the mould together. Hollow block moulds have a removable tapered frame with a handle that sits in the middle to prevent the space filling with mortar. The newly made blocks are kept under cover on platforms to prevent them drying out too quickly in the heat or spoiling in the rain. They should not be moved until they are set. When the blocks harden, then the moulds can be removed and prepared for reuse. They should be cleaned and treated with a mould oil so that the wet mixture does not stick to the sides. 1. very poor thermal insulation; 2. very poor sound insulation; 3. they are difficult to decorate internally because they require an internal lining to attach fixtures and fittings; 4. the general appearance does not look as homely as conventional materials. Timber cladding is the other material used for non-load-bearing external walls. The structural framework consists of a timber roof supported by timber columns on a raft foundation. Lightweight prefabricated timber wall frames are secured to the timber columns. Windows and doors are built into the timber framework as it is made. When all the timber frames are in the correct position, then they are clad with lapped timber boarding. Internally, plas¬ ter board is hung on the framework. Non-load-bearing internal walls The partitions that divide the internal spaces of a building are usually non-load-bearing. When the external walls, roof and floors are in position, then the partitions are constructed by: 1. building them off the floors; 2. pinning them to the ceiling; 3. joining them to the external walls. Non-load-bearing external walls The external wall of a building provides weather resistance and must be durable and fire resistant even if it is not built from load-bearing materials such as brick, block and stone. Corrugated iron Non-load-bearing partitions that are built off solid ground- or first-floor slabs are built quickly and easily. If the subfloor is timber you may need additional support depending on the direction of the span of the floor joists. The two main types of non-load-bearing internal walls are: 1. concrete block partitions (Figure 9.27); 2. timber partitions (Figure 9.28). 71 Walls Head of blockwork between the ceiling joists 3E Noggin to secure the head of the partition between the ceiling joists Timber lintel Door opening Blockwork built off the sole plate Finished floor levels Blockwork built off concrete Sole plate § \ZmZ2ZZZSZL ”T Concrete floor * - o' :y Timber floor Double joists below the partition Figure 9.27 Non-load-bearing concrete block partition walls. partition Figure 9.28 Non-load-bearing timber partition walls. 72 Building construction Concrete block partitions Lightweight concrete blocks reduce the dead weight on suspended floors. Their use makes the building work quick, easy and relatively low cost. One of your main priorities in the construction of internal walls is to make them stable. Figure 9-29 shows you how to place the partitions for maximum stability. This can be done by: 1. placing partitions so that they meet at right angles; 2. making offsets or recesses for the length of a partition; 3. attaching the top of the partition to the main structure. This can be done by forcing drymixed mortar into joints between the blockwork and a concrete slab. 4. nailing noggins, which are short timber pieces, to joists and the head of the partition; 3. placing the partitions so that they run the same direction as the joists; 6. if the partitions run at right angles to the joists, then building up the gap between the angles. Partitions that are built off concrete subfloors can be set out and constructed like any masonry wall. If the subfloor is timber, then you need to consider the direction of the joists. A partition requires two joists beneath it if the floor joists run parallel to the partition to provide adequate support. If the partition is at right angles to the joists, then a timber plate (50 mm x the thickness of the partition) is laid across the timber board¬ ing underneath the blockwork. This spreads the weight over the joists and prevents over¬ loading the floor boards. Tying the partitions into the external walls Partitions need to be tied into external walls. This can be done in two different ways; block bonding the partition blocks, or attaching the partition with metal ties to the external wall. Block bonding (Figure 9.30) is the method of making recesses in the external wall to take the ends of the alternate courses of blockwork from the internal partition. The ends of the blocks are cemented into the recesses. This is a very solid way to fix partitions, but it requires early prepara¬ tion of the external wall so that the recesses are in the right place or you must cut into the blocks after they are built. This can damage the stability of the external walls. Attaching metal ties to the joints of the exter¬ nal wall is the second method. The ties are at¬ tached to the external wall after it is built and tied into the partition blockwork while it goes up. This is the easiest method if the external wall is blockwork. Creating wall openings Figure 9.29 Placing partitions for maximum stability. The door frame or lining is supported in its correct position before the blockwork is built. As the internal partition goes up, you fix metal fastenings to the back of the lining or frame and build it into the courses of blockwork. You need at least two fastenings on each side. If you fix the lining after the blockwork is finished, then you attach it to plugs, which are pieces of wood or plastic in¬ serted into walls to take nails or screws, in the blockwork. You can take the linings up to the soffit of the ceiling and install a glazed panel over the door to 73 Walls let in more light and cross-ventilation. If you put more blockwork over the door, then you need a simple timber lintel to support the small amount of weight. The timber surface should be covered with expanded metal to form a base for plaster and to reinforce the joint between the blocks and the timber. This prevents cracking. The alternative is to use a concrete lintel. Recess left for Timber partitions Timber partitions are also called stud partitions. Timber partitions are built up in stages. Figure 9.31 illustrates a detail of a stud partition where it ties into a door frame. The first stage is the construc¬ tion of the timber framework which consists of: 1. the sole plate. This is the bottom horizontal timber that is fixed to the floor and indicates the position of the partition; 2. the studs. These are the vertical timbers spaced at 400 or 600 mm intervals that are nailed to the sole plate and the head; 3. the head. This is the horizontal timber at the top of the framework that is nailed to the structure above it. The studs fit tightly between the sole plate and the head; 4. the noggins. These are short, horizontal timbers that are secured in position by nailing through Figure 9.30 Block bonding a partition to an external brick wall. Door Stop Lining Stud Architrave Skirting Sole plate Screed Concrete floor Figure 9.31 A detail of a stud partition tied into a door frame. 74 Building construction the studs. The noggins stiffen the studs and provide extra support. Wiring for telephones and electricity should be installed inside the timber framework be¬ fore the boards are fixed. You can feed the wires through the timbers by notching or drilling holes in them. Water pipes should always be accessible. For this reason, you should not enclose them within the partitions. When the timber framework is erected, then you can cover it with boards (Figure 9-32). Well-placed studs will reduce cutting and waste when you fasten the boards to the framework. When vertical joints appear, the joint should be filled or dis¬ guised. Two types of board are good for cladding timber framework: 1. plasterboards; 2. timber. Plasterboards are usually 2400 x 1200 x 12 mm. They are fixed to the framing with galva¬ nised nails. The joints between the boards are: 1. reinforced with paper tape or scrim; 2. filled level with the surface; 3. rubbed down. it is helpful to apply a 3 mm skim coat of plaster first to conceal the joints. Timber cladding usually consists of plywood, chipboard or hardboard panels. They are nailed or screwed to the framework so that the heads of the nails or screws are below the surface of the board. The holes should be filled so that the surface of the board is even. Since the vertical joints are not filled you can cover them in two ways: 1. applying cover strips over the joints and secur¬ ing them to the boards or frame; 2. leaving 3 to 10 mm gaps between the boards to form recessed joints. Stud partitions have advantages and dis¬ advantages compared to block partitions: The advantages are that: The erection of the partitions is a dry pro¬ cess. The partitions are adaptable and can be fitted into awkward places. The materials are very portable and need less storage space than block work. The stud partitions weigh less. The stud partitions are usually cheaper. The disadvantages are that: Stud partitions do not insulate sound as well as block partitions. Fire-resistance is only about half an hour. You can decorate plasterboard immediately, but Head CHECK YOUR UNDERSTANDING Figure 9.32 Parts of a timber stud partition. Walls can be load-bearing or non-load-bearing. Masonry walls should be bonded to provide strength and stability. Masonry consists of natural and manufactured materials. Mortar aligns and binds the masonry into a solid mass. Walls must be built perfectly vertical. The horizontal beds for walls must be level. The opening in a wall must have a lintel or arch to support the masonry above. A lintel can be made from concrete or timber. An arch depends on compression forces for its strength. A concrete lintel can be cast in situ or precast. Brickwork above and below ground must be separated by a damp-proof course. 75 Walls Timber frame walls can be used internally and externally. REVISION EXERCISES AND QUESTIONS 1 2 What are the main functions of: i) load-bearing walls ii) non-load-bearing walls? Draw a diagram to show how you make a concrete block using a timber mould. 3 4 5 6 7 8 What are the materials and mixes that you can use to make two different types of cementbased block? What is the function of a damp-proof course? What is the purpose of a closer in a brick wall? Draw a semicircular brick arch and label the parts. How do you position the first bricks correctly on a strip foundation? What are the advantages of cavity wall con¬ struction? Introduction The fireplace provides a safe fireproof location to burn fuel for heat or cooking. It is connected to the flue, which conducts the products of combustion outside in a safe manner. You can see Figure 10.1 for an illustration of the principles of a fireplace. This chapter tells you about the main parts of a fireplace and flue, as well as how to build them safely. Technical words for parts of fireplaces and flues This list defines some of the technical words that you need to know for parts of fireplaces and flues. Figure 10.2 illustrates some of the main parts. Back a vertical brickwork surface that provides the opening for the construction of the fireplace. Breast the brickwork that forms the part of the fireplace and flue structure that projects into the room. Chimney the brickwork structure that carries the flue above the roof. Fireback a heat-resistant material that lines the brick opening for the fireplace. Flue i) the opening inside the chimney that takes hot air, smoke or flames outside; ii) a flue can also be a separate pipe that links to the chimney in self-contained appliances such as boilers. Gathering the opening in the fireplace where the hearth narrows to the size of the flue. Head the top of the fireplace opening, which is formed by a concrete or stone lintel or a brick arch. 76 200 mm x 200 mm flue The flue lining prevents hot gases and flames entering the building The throat increases the speed of the heated air and combustion gases Hot combustion gases rise by convection Air is drawn into prevent smoke flowing into the room The flame is caused by the conversion of oxygen to C02 Combustion fuel Air flows to the base of the fire Figure 10.1 How a fireplace works. 77 Fireplaces and flues Hearth the fireproof horizontal base of the fire¬ place. Any combustible material such as timber joists must be separated from the hearth by a 50 mm air gap. Jambs usually projecting brickwork at each side of the fireplace opening that can provide adequate depth for the fireplace construction. They should be at least 215 mm of incombustible material. Rendering the cement and sand flue lining that seals the brickwork from leaking flue gases. Ren¬ dering is also called pargetting. Throat a restrictor at the head of the fireplace that increases the velocity of the hot gases in the fire and the air flow to the burning fuel. Chimney Flue Rendering The dimensions of brick fireplaces and flues A brick fireplace and flue should have the mini¬ mum dimensions shown in Table 10.1 for stability and efficiency. Breast Gathering Table 10.1 Minimum dimensions for fireplaces and flues Throat Jamb Fireback Concrete hearth Part of the structure Minimum dimensions (mm) Opening for the flue 215x215 Flue surround 102.5 brickwork around it Brick chimney 425 x 425 Chimney stack projection into the room on external wall (Allow the width of the wall plus a half skin of brick) 317.5 (215 + 102.5) Fireplace opening (Wood burning) 900 Jambs 215 (each side of the opening) Hearth 500 projection 150 each side of opening For a typical fireplace the dimensions (in mm) are: Brick breast Fireplace opening Fireplace foundation First-floor flue and chimney Hearth Figure 10.2 Parts of a fireplace. 317.5 x 1325 900 x 600 467.5 x 1625 425 x 425 1250 x 500 (in front of jambs) 78 Building construction Precast concrete coping These dimensions are important when the chim¬ ney emerges from the roof: 1. The top of the chimney should be at least 1 metre above the roof to keep heat away from the roof covering. 2. Windows should not open closer than l metre below the top of the chimney to prevent fumes entering rooms. The flue should be straight, but this is not always convenient. If you have to offset the flue, then the slope should be less than 30 per cent from the vertical to ensure a good flow of the flue gases (Figure 10.3). At the top of the flue, a concrete cover raised above the opening will keep out the rain. Building a fireplace and flue First you need to construct the foundations and build up the brickwork to ground-floor level. Chap¬ ter 8 has more information on how to do this. Table 10.2 describes how to continue building up from the floor level. Stepped flashing Figure 10.3 The structure of an offset flue. Figure 10.4 Detail of a watertight roof junction. Fireplaces and flues Table 10.2 How to build a fireplace and flue Step Action 1 If the floor is timber: support the hearth with walls and hardcore fill standing on the foundations; trim the floor where it meets the hearth so that the timber is more than 50 mm away; continue with step 3. 2 If the floor is concrete: build the jambs; fix a lintel across the opening to carry the brickwork. 3 Form the throat behind the lintel or shape the lintel to form the front edge of the throat. 4 Build the brickwork so that it gradually narrows to the size of the flue. 5 Build up the chimney breast with the flue opening in it. 6 Render the flue with cement and sand. 7 If the chimney goes through a suspended timber floor at the first floor level, then trim the timber so that it is more than 50 mm away. 8 Trim any timbers in the roof space. 9 Render the external surface of the chimney in the roof space. 10 Make the junction of the chimney and the roof watertight (Figure 10.4): insert a gutter at the back of the chimney; insert stepped metal flashings and soakers between the chimney and the roof covering at the side; insert a metal flashing over the roof covering at the front. slopes inward to meet the throat. It protects the brickwork and increases the heat from the fire. When the construction is completed, you should install metal baskets to hold the fuel. They raise the fuel off the hearth and improve combustion. CHECK YOUR UNDERSTANDING A fireplace is a safe place to make a fire. A flue is a pipe that safely conducts hot air, gases and smoke outside the building. The throat narrows the flue entrance. This in¬ creases the flow of gases, which improves the efficiency of the fireplace. The flue rendering prevents the entry of gases and flames into a room through the brickwork. The hearth projects into the room to protect the floor finish from hot ashes. Timber must be trimmed around a flue, not built into it. • Flashings protect the chimney from rain and protect the roof covering from the heat of the chimney. REVISION EXERCISES AND QUESTIONS 1 2 Finishing off the fireplace You can line the fireplace with a special angled fireback that lines the two sides and back and 79 3 4 Set out a fireplace with a 900 mm opening and a concrete hearth. What is the purpose of the: i) throat ii) gathering? How much should you trim a timber floor around a hearth? Draw an example of a stepped flashing. Introduction The main functions of floors are: 1. to support the loads from the finishes, people, machines, furniture and fixtures; 2. to provide a level surface for normal uses in a building; li u u lT -*— Floor boarding Timber joist 80 3. to provide a level surface for any floor finishes that are applied. Floors are normally classified as: ® ground floors; 9 upper floors. 81 Floors Ground floors are either concrete slabs laid di¬ rectly on the ground on hardcore beds or sus¬ pended timber structures supported on honey¬ comb sleeper walls that stand on concrete slabs. Upper floors are either reinforced concrete slabs or suspended timber structures that are supported on load-bearing walls. This chapter describes these different types of floor and their construction in detail. The difficulty with suspended timber floors on concrete oversite slabs is that you need to take extra care to achieve the three conditions. The space under timber floors at ground level must be well-ventilated and the timber treated with pre¬ servative to ensure that it stays dry and is resistant to insects such as termites. Because access is awk¬ ward it is difficult to observe and control potential problems. The oversite concrete slab Concrete ground-floor slabs At ground-floor level, the concrete slab that rests on the ground must: You can build three different types of concrete ground floor: 1. provide a total barrier to dampness in the ground by the use of a damp-proof membrane; 2. prevent termites from entering the building; 3. prevent the growth of vegetation. 1. an oversite concrete floor below a suspended timber floor (Figure 11.1); 2. the ground-floor slab in a brick or masonry building; 3. a raft foundation in a timber frame building (Figure 11.2). Concrete oversite slabs are used for both sus¬ pended timber floors and concrete floors. 82 Building construction The construction is similar for each type. You need to provide: a hardcore bed; • a blinding; a damp-proof membrane. Raft foundations also need steel reinforcement. The blinding The finished hardcore has a rough, open-textured surface that you must make smooth before laying the damp-proof membrane. You do this by laying about 50 mm of sand, ashes or a weak, dry con¬ crete slurry called blinding over the surface of the hardcore. You should carefully level the surface and inspect it to see that there are no sharp projections. The hardcore bed The purpose of the hardcore bed is to: 1. provide a free-draining bed that will keep the concrete slab warm and dry; 2. resist the growth of vegetation; 3. provide a level base for the oversite concrete. The hardcore bed consists of material that resists crushing, such as broken brick, stone or rock. The pieces should be large enough to ensure plenty of space so that moisture isn’t trapped within the hardcore. You put down layers that are about 150-200 mm thick and flatten them by hand with a tool called a rammer to consolidate them. You can also use a machine called a plate vibrator for large areas of hardcore. Figure 11.3 Damp protection for an exposed wall. The damp-proof membrane (dpm) The membrane’s purpose is to prevent dampness entering the building through the concrete slab. It is usually a heavy-duty polythene sheet that is tough enough to be handled on a building site without tearing or puncturing. The material should stay intact even when workers walk over it while they fix reinforcement in the floors and lay concrete. You should lay the dpm so that the edges over¬ lap the joints. The edges of the dpm must also overlap the edges of the dpc in the walls as shown in Figure 11.3. 83 Floors Laying an oversite concrete slab A typical oversite concrete floor slab that is laid directly on the ground is made from concrete mixed in these proportions: 1 part cement; 3 parts sand; 6 parts water. Since concrete shrinks as it dries you should lay it in areas that are no larger than 3 metres by 3 metres or 10 square metres. The raft foundation slab Ground-floor slabs that are also raft foundations may have steel mesh reinforcement in the slab and the edge beams. You begin by excavating the shape of the edge beams, which stiffen the raft in the formation level. Table 11.1 gives the dimensions of a raft founda¬ tion that, could support a simple one-storey building. Table 7 7.7 Dimensions of a raft foundation Part of foundation Example Divide an oversite slab that measures 12 x 6 m into eight areas that each measure 3 x 3 m (Figure 11.4). Divide the floor area into sections with timber boards that are the depth of the floor slab. The boards should be fastened with small mounds of concrete so that they do not damage the dpm. If you concrete more than one section at a time, then you must ensure that you do not concrete adjacent bays at the same time. You should pour the concrete in a chequerboard pattern so that you can fill in the spaces left after shrinkage as each section dries. Figure 11.4 Laying the oversite concrete into bays. Dimension (mm) Foundation thickness 100 Edge beams 250 x 350 Reinforcement bars Two or three at 10 mm You follow these steps to make a simple raft foundation slab: 1. Spread hardcore and blinding in the measured area. 2. Lay the dpm over the blinding. 3. Build vertical formwork on struts along the out¬ side position of the edge beams to contain the concrete. 4. Lay the reinforcement, the mesh for the slab and the bars in the edge beams in position. 84 Building construction 5. Support the reinforcement 25 mm above the dpm by fixing cement spacers underneath the bars so that the concrete can flow all around them. 6. Divide the area into 3 metre by 3 metre bays (Figure 11.4). 7. Fix boards over the reinforcement to prevent the concrete leaking out. 8. Pour the concrete so that it fills all the spaces on the slab (you can use a mechanical vibrator to do this properly). Curing the concrete When you complete the construction of the oversite concrete slab or the raft foundation, you then leave it to cure for seven days. Curing is a controlled process for keeping the newly laid concrete just moist enough to dry out without shrinking or cracking. If the concrete slab is laid early in a contract, then it may be exposed to the rapid drying effect of the sun and wind unless you use these methods to keep it moist: 1. Lay polythene sheets over the concrete and keep them in place with bricks around the edges and along joints. 2. Inspect the slab every morning and spray it with water if necessary. 3. Use hessian mats as an alternative. They need to be sprayed with water every day to keep them damp enough. Normally you can remove the covering after seven days. This timing does depend on local conditions. A cured slab is ready for the next stage. The alternatives are: 1. no further treatment if the slab is the finished floor for a garage or storeroom; 2. laying a screed if the slab is to have a separate floor finish; 3. building a base for honeycomb sleeper walls to support a timber floor. Building a suspended timber floor You make the solid concrete oversite slab first. If the space between the timber floor and the oversite slab is well-ventilated you can omit the dpm. To build a timber floor you will need: honeycomb sleeper walls; air bricks; a damp-proof course; wall plates; floor joists; floor boarding. These elements of a timber floor are described in the following sections (Figure 11.1). Honeycomb sleeper walls Honeycomb sleeper walls are brick or block walls built over the oversite concrete so that air can circulate freely in the gap to all parts of the under¬ floor. You construct them by omitting bricks across the width of the external walls. These steps de¬ scribe the process: 1. Set out a row of stretcher bricks embedded in mortar on the oversite concrete. 2. Leave a header space between each stretcher. 3. Lay the next course so that each brick is centred over the space below. 4. Continue these steps for three or four courses. 5. Bond the ends of the courses into the external walls. Airbricks Airbricks are special bricks with holes in them that allow air to flow through. Build the bricks, which are the height of two normal bricks, into the exter¬ nal walls at opposite sides of the building. Fix them at 2.5 metre intervals. Mesh fly screens will keep out insects. Damp-proof course (dpc) A dpc is usually bituminous felt laid on the sleeper walls in widths of 102.5 mm to prevent dampness entering the wall plate. Wall plates Wall plates are timber pieces about 75 x 100 mm that are used as bases for fixing floor joists. They are laid carefully on the dpc along the length of the sleeper walls. Floor joists The floor joists are the pieces of timber that span between the wall plates and support the floor boards. The size of the joists depends on the spacing of the sleeper walls. Table 11.2 is a guide to the appropriate lengths for joists that are spaced 400 mm apart. Judging the length of the joists 85 Floors correctly will reduce waste and time spent cutting the timber. Table 11.2 Joist dimensions Span (mm) Joist size (mm) Joist length (mm) 1200 38 x 75 3800 1800 38 x 100 3100 or 4800 2000 50 x 100 4100 You attach the joists to the wallplates by nailing through the sides down into the wallplate. If the joist is not long enough to span the external walls, then two pieces should be lined up and fastened at the wallplate. You should try not to fix too many joists to the same wallplate, but stagger them over the slab. Joists are not built into the external walls be¬ cause the ends would be exposed to moisture and could rot. The preferred fixings for external walls are: wallplates attached inside the external wall; galvanised joist hangers; brick or block piers. Timber flooring The type of timber flooring that you use depends on availability and preference. Standard choices are: softwood boards; plywood; blockboard; chipboard. The following sections describe these types of floor in more detail. Softwood boards Softwood boards should be at least 25 mm thick and less than 100 mm wide. This reduces the shrinkage gaps between boards and the possibility of distortion. The boards are usually joined at their plain edges and nailed to the joists using oval wire nails that are 2.5 times longer than the thickness of the board. You use a hammer and punch to drive the nails below the surface of each joist. You need to judge how much the boards are likely to shrink after they are laid. To force the boards closely together you should fix a temporary batten across the joists. Then drive a pair of folding wedges along the edges of the boards. This pushes the boards tight against their neighbours so that they can be nailed in position. You can also use tongue and groove boards. These boards have a projecting tongue about 10 mm wide on one length. The other length has a groove about 12 mm wide. You can fit a tongued edge into a grooved edge as you lay the boards. They should also be wedged to push them tightly together. You can nail tongue and groove boards through the top or use secret nailing. In this method you nail the side of the board above the tongue. The next board then covers the nails in the first board when it is laid beside it. Other types of timber boards You can use three other types of timber board for floors: plywood; blockboard; chipboard. Most boards are manufactured in a standard size of 2400 x 1200 mm. You should always check that the board thickness is adequate for the spacing of the joists. Upper floor construction Upper floors should not span more than 5 metres in simple buildings. The two most common types of construction for upper floors are: 1. timber floors (Figure 11.5); 2. reinforced concrete floors (Figure 11.6). Both types of floor may need additional support for larger spans. Timber floor construction A first-floor span of 5 metres is the limit for simple timber floor construction in a small building. Your local authority’s building regulations may have guidelines for the size of timber joists, but Table 11.3 shows the maximum practical limit. 86 Building construction Figure 11.5 The structure of a timber suspended floor. Figure 11.6 The structure of a reinforced concrete floor. 87 Floors Table 11.3 Structural limits for timber floors Structural part Structural limit Joist 225 x 75 mm Span 4.8 metres at joist intervals of 400 mm Load 0.5 - 1.0 kN/m2 The size of joists depends on: 1. the span from support to support; 2. the spacing between joists (which is usually 400 mm from centre to centre); 3- the quality of the timber; 4. the total floor load, which is about 1.0 kN/m2 in domestic buildings. The joists are placed on the external wall at the correct height. A wall built from 215 mm bricks gives the joists a 100 mm bearing with a half brick thickness covering on the end. If the joist is 50 mm, then it needs a brick and a half to fill the space between adjacent joists. The ends of the joists should be treated with creosote or other preserva¬ tive before they are built into the wall. An alterna¬ tive method is to support joists on galvanised steel joist hangers. They have shoes to fit around the ends of the joists. The shoes hang from straps placed over steel hooks in the brick or blockwork. Joist hangers are a fast way to suspend joists and use less timber. Figure 11.7 Trimming joists at an opening. Trimming a staircase opening A staircase will go through the first floor. Since you must form an opening, you will need to cut into the joists. The joists around the opening are called: trimmed joists (they are shortened by the opening); trimmer joists (they support the trimmed joists); trimming joists (they support the ends of the trimmer joist). This type of work is expensive and must be done very carefully to minimise damage to the joists. The main principle is to join the end of the trimmer joist very firmly to the trimming joist because the load is greatest at that point. You can use a metal hanger or a housed joint in the upper half of the joist to avoid cutting into the trimming joist. You can see the layout around an opening in Figure 11.7. Making struts The joists may bend under the load if the span is between 3 and 5 metres. A twisting joist can weaken the floor. You can use struts to stiffen the entire floor structure. There are two methods for making struts: 1. herringbone, which consists of two lengths of Building construction 88 50 x 50 mm timbers fixed so that they criss-cross the top and bottom edges of the joists and are nailed in the middle to make a herringbone pattern; 2. solid, which consists of a number of pieces of 38 mm timber of similar depth to the joists. They are cut to fit tightly between adjacent joists and are skewnailed. The solid pattern is cheaper, but less effective than the herringbone pattern. Struts are usually fixed in the middle of the span. You fill the gap between the last joists and the wall by inserting wedges along the line of the struts. Floors The types of timber floor that are suitable for upper floors are the same as for the ground floor: # plywood; © blockboard; © chipboard. These floors were described in the section on timber ground-floor construction in this chapter. Reinforced concrete first-floor construction Most reinforced concrete suspended floors are cast in situ. Two forms of construction are possible: 1. a solid concrete slab with main reinforcement that spans the shortest distance with secondary reinforcement that spans the longer distance; 2. a hollow pot floor with beams that span the shorter distance only. (a) No sag or deflection (b) Top half o : the slab compresses compression or tension Th e bottom half stretches —y _ E zA -W~~ -w-W-w-—▼ • 1 :U'Jt-'-r.- ■-W ^ The amount of deflection (e) Compression zone LOAD Tension zone Tension stress is absorbed by the steel reinforcement o Neutral axis Figure 11.8 The principles of deflection in concrete: (a) a concrete slab without loading; (b) loaded concrete deflecting under the load; (c) putting steel in the bottom of the slab; (d) an unreinforced slab is impossible to use; (e) a reinforced slab makes suspended concrete construction possible. 89 Floors The thickness of the concrete and size and distribution of the steel reinforcement bars are complex issues that depend on the distance to be spanned. You should use a structural engineer to do the calculations before construction begins. General principles of the design of reinforced concrete suspended slabs: Concrete is strong when compressed, but weak under tension. It should be rein¬ forced where subjected to tension. Concrete sags or deflects when it spans between supports. This creates compres¬ sion in the top half of a slab and tension in the bottom half. Steel reinforcement bars will resist tension if they are built into the bottom of the slab. If the slab is laid continuously over an intermediate support, then the deflection is reversed. The tension moves to the top of the slab, which then requires the steel rein¬ forcement. These principles are shown in Figure 11.8. as well as the wet concrete. You can follow the steps in Table 11.4 to make the formwork and position the services and rein¬ forcement bars. These steps take you to the point where you are ready to mix and pour the concrete for the slab at the next stage. Table 11.4 Preparing the slab Step Action 1 Use the working drawings to establish the level of the underside of the floor slab. This becomes the level of the top of the formwork deck. 2 Put up the supporting framework of props, ledgers and joists and nail the formwork deck to the joists. 3 Level the entire structure by adjusting the wedges and nail diagonal braces across the props to stiffen them. 4 Inspect the deck for open joints and fill the gaps with building paper or other material. 5 Treat the deck with an oil, which will make it easier to remove the formwork when finished. 6 Attach the electrical conduits for the first floor wiring and ceiling lights for the room below to the formwork. This work should be done by an electrician. 7 Attach any pipes for other services to the formwork. 8 Cut and bend the reinforcement bars as shown on the drawings. Lay them out on the formwork separated at intervals by concrete spacers and tie the bars in position with soft steel wire. Casting a solid reinforced concrete floor First, you need the structural engineer’s drawings to show the layout of the reinforcement bars, the thickness of the concrete and the right concrete mix. With this information, you follow these steps to cast the floor: 1. Erect the formwork. 2. Position the services. 3. Position the reinforcement rods. 4. Mix and pour the concrete. 3. Cure the concrete. 6. Remove the formwork. Each of these steps will be described in more detail in the next sections. Erecting the formwork The first step is to erect the formwork. It provides a level platform to support the wet concrete until it hardens enough to be self-supporting. You make the formwork from timber boards propped up from the floor below by timber supports. The structure must take account of any beams, lintels and openings. It should be strong and stable so that it can support the weight of people and plant Working with the reinforcement bars A solid concrete slab will have main reinforcing bars and distribution bars. The main reinforcing bars are usually 12 mm at 150 mm centres span¬ ning the shorter direction. The distribution bars will be 6 mm at 450 mm centres which span across the main reinforcement. You can use heavier bars over beams and lintels and link them to the main reinforcement with stirrups. At least 25 mm must be left between the bars and the bottom of the slab for a thick coat of concrete to provide fire-resistance and prevent the reinforcement rusting. If you plan to build a reinforced concrete stair¬ case you need to leave starter bars, which project 90 Building construction into the staircase opening. These bars let you tie the staircase into the slab as you build. Mixing and pouring the concrete A typical mix for a reinforced slab is 1:2:4: Just like the solid concrete ground floor slab, the wet concrete must be covered and kept damp for seven days. This was described in more detail earlier in this chapter. The formwork is left in position until the con¬ crete hardens. It is safe to remove it after 14 days. 1. one part cement; 2. two parts sand; 3. four parts coarse aggregate. The water/cement ratio should be 0.5. In Chap¬ ter 21 you can read about concrete mixes in more detail. You pour the concrete in one operation to avoid joints in the slab. Before you start to pour, you should put some small mounds of concrete on the formwork deck and level them off to the thickness of the finished floor slab as a depth guideline. You then need to carry the concrete up to the first floor level. It should be spread quickly, con¬ solidated with a poker vibrator to ensure that the reinforcement is completely covered in concrete and levelled with a wood float. Making a hollow pot reinforced concrete floor Hollow pot floors use clay pots to reduce weight so that they are lighter than solid floors. The pots are 300 x 300 mm. They vary in thickness depend¬ ing on the depth of floor required by the design. When you look at the section of a hollow pot floor in Figure 11.9 you can see that the concrete forms a T-shape. The concrete at the top of the floor is under compression while the steel at the bottom takes the tension forces. Opening for the stairs Figure 11.9 The structure of a hollow pot concrete floor. Hollow pots laid on decking 91 Floors Your procedure for making a hollow pot floor is to: 1. erect the formwork; 2. position the services; 3. put the hollow pots in position; 4. place the steel reinforcement; 5. mix and pour the concrete; 6. cure the concrete; 7. remove the formwork. Most of these steps are a repeat of the procedure for making a solid concrete floor. The steps that differ are setting the pots and putting in the steel reinforcement. You should set out the pots in straight rows across the deck. Leave a space that measures 100-150 mm between the rows. Then place the steel reinforcement bars in the centre of the spaces between the pots. Use spacers to keep the bars off the deck so that the concrete can flow underneath. Concrete slabs at ground level can be: i) an oversite floor slab ii) a slab that supports sleeper walls for a timber floor iii) a raft foundation. Curing concrete controls the rate of the loss of moisture and resists cracking through shrinkage. Suspended timber floors must be well-ventilated underneath. Joists are used for the construction of timber floors. The size of the joists varies with their spacing and span. Concrete is weak under tension. Steel is used in reinforced concrete because it is strong under tension. Hollow pot floors save concrete and reduce the dead weight. REVISION EXERCISES AND QUESTIONS 1 2 CHECK YOUR UNDERSTANDING Floors can be supported by the ground or sus¬ pended off it. Suspended floors span between supporting walls. • Floors can be made from timber, mass concrete or reinforced concrete. • Concrete slabs on a damp-proof membrane pre¬ vent the entry of moisture into the building. • Timber can be attacked by insects and moisture. 3 4 5 6 What are three uses for an oversite concrete slab? What is the purpose of a honeycomb sleeper wall? i) Draw an example of an oversite concrete slab which measures 16 x 13 m. ii) Show the order that you should pour the concrete to prevent excessive shrinkage. How is a wet concrete slab consolidated and cured? What is the purpose of steel reinforcement in a concrete floor slab? How should you trim a timber staircase around a staircase opening? Introduction A roof on the top of a building fulfils important functions like: Roofs should meet these basic standards of per¬ formance: 1. keeping out the rain and wind; 2. providing shade from the sun; 3. keeping the interior cool; 4. retaining heat in cool weather; 5. ensuring that the structure is properly weighted down. 1. allowing rainwater to flow freely away; 2. expanding and contracting without failure; 3. resisting fire adequately; 4. providing light and ventilation; 5. durability. Figure 12.1 A tiled roof on a modern African house. 92 93 Roofs Figure 12.2 The main parts of the structure of a pitched roof. The two main types of roof which you will read about in this chapter are: 1. pitched roofs; 2. flat roofs. Figure 12.1 is a photograph of a typical pitched roof on a house in Southern Africa. Technical words for parts of a roof The main technical words used in roof construc¬ tion are defined in this section. Figure 12.2 illus¬ trates the main parts of a roof. the external material that is laid over the roof structure to protect the inside of the Covering building. Coverings can be: O asphalt; • bituminous felt; • corrugated mineral fibre sheets such as fibre cement; • corrugated metal sheets such as galvanised iron and aluminium; • thatch; • plain tiles; • interlocking tiles. Eaves the bottom end of the roof where it meets the wall. Fall the slope required on flat roofs for water run-off. Fascia a thin timber board that is fixed to the end of rafters or roof joists to support the gutters. Hip the point where two inclined roof surfaces meet over an external angle. 94 Building construction Jack rafter . a short rafter that spans the hip and eaves or valley and ridge. Pitch the angle formed by the slope of the roof. Purlin A purlin can be: i) a horizontal timber member that provides sup¬ port to the rafters; ii) a timber member spanning between roof trusses that supports roof sheets. Rafter the timber member that spans from the eaves to the ridge in a pitched roof. Ridge tile a tile that caps the top of the roof. a timber at the apex of the roof that takes the tops of the rafters. Soffit the horizontal board that can be fixed to finish the roof structure at the eaves. Span the horizontal distance between the sup¬ ports of structural members such as the rafters. Valley the point where two inclined roof sur¬ faces meet over an internal angle. Verge the edge of a roof that meets a gable wall. Wall plate the timber member fixed to the top of a wall to secure a flat roof joist or rafter. Ridge Figure 12.3 Examples of different common roof types: (a) gable roof; (b) lean-to roof; (c) mono-pitch roof. 95 Roofs Pitched roofs A pitched roof is often a popular choice. The main supporting structure is timber, which is easy to work and transport. A pitched roof is stable in most weather and its slope disposes of rainwater quickly. Additionally, the space enclosed by the roof can add some extra living or storage space. Types of pitched roof In simple roof construction you will usually find these types of roof: 1. Gable roof In this type of roof the ends of the roof enclose the end walls. The triangular wall between the roof verges is called the gable end. 2. Hipped roof A hipped roof is formed when two roof slopes meet at right angles. 3. Lean-to roof This roof has a single pitch that rests against a higher wall. 4. Mono-pitch roof This roof has a pitch in one direction. The ridge does not rest against any¬ thing. Some of these roof types are illustrated in Figure 12.3. Parts of a pitched roof Three parts of a pitched roof affect the structural design: 1. span; 2. pitch; 3. roof covering. Span The span is the distance between the masonry structures that support the roof. The structure of the roof becomes more complex as the span in¬ creases. Pitch The pitch is the angle of the slope of the roof measured from the horizontal. A steeper pitch needs more roof covering material, which increases the weight to be supported. The surface area af¬ fected by wind is also greater. The roof needs to be strong enough to allow for these factors. Roof covering The roof covering material varies from lightweight sheets that weigh about 12 kg/m2 to plain clay tiles that weigh 65 kg/m2. Different methods of pitched roof construction Pitched roofs can be built in different ways de¬ pending on the loads and sizes (Figures 12.4 and 12.5). This list describes some common types of pitched roof that use different methods of con¬ struction. Couple roof A couple roof has two timbers (called rafters) that are joined at the apex at their top end and rest on the walls at their bottom end. A couple roof is used for small spans. Closed couple roof In a closed couple roof a tie member connects the bottom ends of the rafters. This design stiffens the rafters to resist the loads on a larger span. Collar roof The collar roof has a tie member to connect the rafters higher up the slope. This design allows the roof eaves to be lower or the ceiling to be higher. Purlin roof A purlin roof has a horizontal timber that is sup¬ ported by the external walls of the roof structure to stiffen the rafters. The purlin may be supported by struts, which rest on internal load-bearing walls. Trussed purlin roof Trusses replace struts as support for the purlins (Figure 12.6). Trusses, which are spaced about 1800 mm apart, are braced against external walls rather than internal load-bearing walls. Trussed rafter roof A trussed rafter roof combines ceiling joists with additional struts and ties for larger spans (Figure 12.7). The trussed rafters, which are prefabricated, are braced against the external walls. The use of trussed rafters eliminates the need for purlins and other supporting timbers. The structure of a timber pitched roof A typical timber pitched roof such as the one in Figure 12.8 has this structure: 96 Building construction (c) Ridge Figure 12.4 Types of pitched roof: (a) couple; (b) closed couple; (c) collar. 97 Roofs Gable wall Figure 12.5 Purlin roof. 1. rafters spanning between the wallplate and ridge with support from purlins; 2. ceiling joists spanning between the wallplates with support from special purlins called binders; 3. roof trusses spaced at 1800 mm intervals; 4. purlins spanning between the trusses. The rafters span the wall plates and ridge. They form the supporting framework for the roof cover¬ ing, so their size must relate to the length of the span and the spacing intervals between them. „ Rafters that measure 50 x 125 mm are the most cost-effective. If the roof design requires larger rafters, .then you should use purlins in the roof construction to support the rafters and minimise the size required. The ceiling joists support the ceiling below the roof space. When you attach the joists to each end of the rafter at the wallplate, then they become a tie. This creates the classic triangular roof shape with two rafters and a tie at the bottom. If a ceiling joist spans too great a distance, then you need to support it with a special purlin called a binder. Purlins, which should be less than three metres long, need support from struts that are braced against internal load-bearing walls. Since these walls are expensive to build, you can use the trussed purlin roof (see Figure 12.6) as an alternative. The purlins span between the roof trusses and the trusses span between the external walls. You can use a prefabricated trussed rafter roof to avoid the construction of internal load-bearing walls (Figure 12.7). Each rafter forms a truss that spans between the external walls. The ceiling joist ties the bottom of the truss so that you do not use 98 Building construction Ridge Rafter Purlin Ceiling joist or tie Binder Wall plate Figure 12.6 Trussed purlin roof. purlins or binders. A crane lifts this roof into position on top of the walls. Notes on trussed rafters • All the trusses are prefabricated, so they should conform to the specified size. The trusses are the same thickness, but their depth may vary. $ They do not have any projections so they can be transported and stored compactly. • Trusses can span up to 12 metres in a basic ‘W’ shape. Trusses are an economical use of timber. • They are designed for evenly distributed loads. They shouldn’t be cut or changed. Small trusses will have members 38 or 47 mm thick depending on the span. The members will vary between 75 and 125 mm in depth. Trussed roof construction is a fast method of roof construction. Connecting the trusses Special methods for connecting trusses have been developed because simple nailed timber joints are not strong enough. The bolted metal connections shown in Figure 12.9 are better. They ensure that the timber joints can withstand their loads. This section describes a variety of connections. Split-ring connectors These connectors are embedded in timber mem¬ bers which are side by side. One half of a ring connector on one member fits into a circular groove cut into the other member. The load on the timber joint is carried by the area of the ring surface. Gang nail plates (Figure 12.9) These plates are galvanised steel plates with pro¬ jecting nails. They are placed across the truss members to be connected and the nails are forced in under pressure. You put a plate on each side of the joint. Rafters Figure 12.7 Trussed rafter roof. Figure 12.8 Parts of a timber pitched roof. 100 Building construction A connector and bolt joining three timber pieces Figure 12.9 Truss connections. 101 Roofs Plywood gussets (Figure 12.9) Plywood is strong enough to form the joining plate for truss construction. The gussets, which are the pieces of plywood that join the timbers, are cut and shaped to fit over the trusses. They are then glued and nailed to fix them securely in position. Using tiles as roof coverings Roof tiles are usually made from clay or concrete that is moulded into suitable shapes. Their function is mainly to keep the roof watertight. The tiles are overlapped so that the rainwater flows down the slope of the roof and the roof structure underneath remains dry. Tiles do not fit closely enough to prevent the wind entering the spaces between them. Since rain could be driven underneath the tiles you need to insert a layer of polythene or felt over the rafters. If water finds its way through the tiles, then it will flow down this layer into the gutter. The choice of tiles will depend on the design of the roof. This section describes some of the most common types, which are plain tiles and interlock¬ ing tiles. Nibs for placing the tile on the tiling Plain tiles (Figure 12.10) Plain tiles are the simplest type of manufactured tile. A simple rectangle about 265 x 165 mm, these tiles have holes at the top so that they can be nailed to battens. Small projections underneath the tiles help to place them correctly on the battens. Plain tiles will be waterproof under two condi¬ tions: 1. The pitch of the roof must be greater than 35°. 2. The tiles must be double lapped. This creates a weight on the roof of 70-80 kg/m2. Interlocking tiles (Figure 12.11) Interlocking tiles are larger than plain tiles. A typi¬ cal tile measures about 400 x 300 mm. The tiles have special edges to allow them to fit together or interlock. These tiles can be laid in a single lap and remain weatherproof. The completed roof weighs about 40-50 kg/m2. The pitch of a roof constructed with interlocking tiles can be as shallow as 17°. Laying a tiled roof When the shell of the roof is completed, then the Figure 12.10 Plain tile roof construction: (a) example of a plain tile; (b) a plain tile with nibs. framework should be covered with a layer of polythene sheets or felt to keep out the wind and rain while the tiling work is done. These sheets stay in position to protect the roof space from the weather. Your next job is to fix the tiling battens in place. You need to calculate how the position of the battens relates to the size of the tiles. 102 Building construction Fixing the tiling battens You follow these steps to fix standard-sized bat¬ tens (38 x 19 mm): 1. Treat the battens with preservative to prevent rot and insect attack. 2. Starting at the eaves nail the battens to the rafters at the distance calculated for the gauge (using aluminium or copper nails). 3. Finish at the ridge by nailing additional battens if required. 4. Fit a tilting fillet to the eaves. You can see how this looks in Figure 12.12. Laying plain tiles You lay plain tiles in regular bond patterns. The tiles on one course should lie over the joints in the course below. Lay the eaves course first with a shorter tile that does not need the overlap at the bottom. Continue laying courses of tiles until you reach the ridge, where you may need a smaller tile to complete the job as you can see in Figure 12.13. You should nail the tiles to the battens at every fourth course unless the roof is exposed to very strong winds. Figure 12.14 illustrates a detail for plain tiling at the junction of the eaves. You may need special tiles for the: ridge; eaves; hips; valleys; verges on gable walls. Figure 12.11 Two views of interlocking tiles: (a) top view; (b) joint between tiles. Calculating the batten positions You need to calculate the gauge, which is the spacing between the tiling battens. The overlap for plain tiles is about 65 mm. The calculation is: Length of a tile - the overlap , -5---- = the gauge Example 265 mm - 65 mm - . „„ = 100 mm Figure 12.12 A tilting fillet fixed to the eaves. Roofs Figure 12.14 Eaves detail. 103 104 Building construction Laying interlocking tiles Interlocking tiles are also called single lap tiles. They weigh less than other tiles and can be laid on roofs with a very shallow pitch. This allows a wider roof span and uses less timber in the roof Figure 12.16 A detail of a half-round ridge tile. construction. Figure 12.15 is a section to show how interlocking tiles should be laid. After fixing the felt or polythene underlay and treating the tiling battens with preservative, then you need to calcu¬ late the spacing for the battens. 105 Roofs Figure 12.17 Sheet roofing on a pitched roof. Calculating the batten positions You can subtract the overlap from the length of the tile to calculate the gauge for the batten positions. 5. Fix special tiles if required for: ridges; hips; valleys; verges. Example (for a 400 mm tile with 75 mm lap) 400 mm - 75 mm = 325 mm gauge The steps for fixing interlocking tiles are similar to those for fixing plain tiles: 1. Fix the battens (38 x 25 mm) to the correct gauge position. 2. Begin laying tiles at the eaves (no special tiles are required because there is no overlap). 3. Make sure that each tile interlocks with the tile next to it. 4. Finish laying the tiles at the ridge as shown in Figure 12.16. Using roof sheets as roof covering An alternative to tiling a roof is to cover it with sheeting materials like: • corrugated fibre cement; O corrugated galvanised steel. Figure 12.17 shows you the construction of sheet roofing on pitched roofs. 106 Building construction Corrugated fibre cement sheets These roof sheets are made from fibres embedded in cement to produce a strong, durable material. The fibres are firmly bonded in the cement so that they do not produce any health risks during nor¬ mal cutting, drilling and fixing. The usual roof pitch for these sheets is 22°. Since fibre cement sheets weigh about 16 kg/m2 they can span up to 2 metres. Roof construction generally for these sheets is simple. The roof structure uses purlins as the tim¬ bers to support the roof sheeting instead of rafters. The purlins, placed about 900 mm apart on the slope of the roof, are supported by a roof truss that spans the building. The dimensions for fibre cement sheets are 3000 x 600 x 6 mm. Fixing fibre cement sheets Fibre cement sheets are very brittle and will not support a person’s weight on a roof. You need to use ladders or crawlboards to move around the roof or move along the line of purlins. This is the procedure for fixing fibre cement sheets: 1. Position the first sheet in a bottom corner of the roof framework. 2. Drill through a sheet on top of the corrugations (the holes should be more than 73 mm from each end of a sheet). 3. Fix it to the purlins with galvanised iron drive screws and cupped washers. 4. Lay the next sheet so that it overlaps the first sheet by one corrugation (about 150 mm). 5. Continue this procedure until you fix the last sheet. 6. Fix a special ridge member that is in two parts. One part is fixed to each slope and they are bolted together. You need to cut off a top corner and bottom corner on all sheets but the first sheet. This reduces the thickness of the overlapping sheets at those points. You join the sheets so that the two corners meet in a single thickness. Corrugated galvanised steel sheets These sheets are used frequently because they are cheap and quick to put up. They do have dis¬ advantages: 1. They have a short lifespan because they rust when the galvanising is damaged during the fixing. 2. They are noisy when it rains. 3. They heat up rapidly in hot weather. 4. They lose heat rapidly in cool weather. 5. Condensation occurs because of the lack of insulation. The thin sheets do not have any special fixing requirements. The procedure for fixing galvanised steel sheets is the same as for fibre cement sheets. You may want to paint the sheets after fixing to reduce the heat absorption and prolong their life. Flat roofs Flat roofs, which can be timber or reinforced con¬ crete, are popular forms of roofing for houses. Their advantages are: 1. They are very easy to put up. 2. They can create extra usable space if they are accessible. 3. They are easily maintained. Their main disadvantages are that: 1. They lose heat. 2. They are not as weatherproof as pitched roofs. 3. The finishes do not last as long as roof tiles. Principles of building a flat timber roof The structure of a flat roof requires: a deck or slab; a method for disposing of rainwater; a watertight covering; some insulation. The procedure for making a flat timber roof is similar to making a timber floor. The joists span between the supporting walls and boarding is fixed over the joists to form a deck for the water¬ proof covering (Figure 12.18). The main difference is that the deck must have enough slope to get rid of rainwater. You can make the slope by fixing strips of wood called firrings to the top of the joists. The firrings can be different depths or be tapered in the direction of the fall. 107 Roofs Fall Boarding Gutter L -- XI / Firring Joist Fascia / Strutting t 3500 mm Figure 12.18 The structure of a flat timber roof. Calculating dimensions for firring pieces 1 If you want a fall of 1:80 over 3.5 metres, then the difference in levels should be 3500/80 = 43.75 mm. The minimum thickness of a firring piece is 25 mm. The maximum thickness would be 25 + 43.75 mm = 78.75 mm (say 75 mm). If the fall is in the direction of the joists, then the firring pieces should both be tapered from 75 mm to 22 mm. 2 If the fall is across the joists, then the firrings should be the same depth, but their thickness should vary from 75 to 22 mm. It is not practical to lay firrings so that they span the joists because their thin ends will not be strong enough to support a load at the lower end of the slope. 0.6 kN, then the dimensions should be 150 x 75 mm with 400 mm centres. If the roof is used as living space, then the joist size for a similar span could be 175 x 75 mm. How to build a flat timber roof Table 12.1 describes how to build a simple flat timber roof. Table 12.1 Building a flat timber roof Step Action 1 Fix the joists in position by building them into the external walls and supporting them with joist hangers (provide struts if required). 2 Fix the firring pieces. 3 Lay the timber decking and continue building the roof as if you were building a timber floor (see Chapter 11). The use of the roof is a key factor in its design. If people can sit on it, then it must be as strong as a floor. If it is not used as a living space, then the joists can be smaller. The recommendations for suitable joist sizes may be in your building regulations. Building a reinforced concrete roof Example of typical joist sizes If the joists span four metres and support a load of A reinforced concrete roof is built exactly like a reinforced concrete floor slab. It can be solid or 108 Building construction hollow pot construction. You should follow these steps to build a reinforced concrete roof (they are described in more detail in Chapter 11): 1. Erect the formwork. 2. Position the services. 3. Fix the reinforcement. 4. Pour the concrete. 5. Cure the concrete. 6. Remove the formwork. A hollow pot roof is constructed in the same way except that hollow pots are laid on the deck before the reinforcement is fixed. The top of the structural slab for a flat reinforced concrete roof is laid level. The falls are provided by a cement and sand screed that has the correct slope. The falls are calculated in the same way as for a flat timber roof. The structural engineer will calculate the effect of the extra weight of the screed in the roof design. Finishing off a flat reinforced concrete roof The edges of a flat reinforced concrete roof can be finished off by constructing: 1. an overhanging roof that takes the edge of the roof over the surface of the external wall; 2. a parapet roof that extends the edge of the external wall higher than the roof. Gutter Figure 12.19 Two types of flat roof construction: (a) an overhang; (b) a parapet. 109 Roofs Figure 12.20 A detail of a coping on a parapet roof. Combinations of an overhanging roof or parapet roof are possible on the same building, particularly if you build a gutter on one side. Figure 12.19 illustrates these options. Finishing off a parapet roof Copings, which are short sections of concrete fitted together, finish off the top of the exposed external wall of a parapet roof and shed rain (Figure 12.20). They are bedded in a dpc of bituminous felt to improve their water resistance. They should be wide enough to overhang the wall by at least 50 mm. The tops of the copings slope in either one or two directions to shed rain. Brick-on-edge copings can be bedded in two courses of tiles as an alternative method for finish¬ ing a brick wall at roof level. Waterproof roof finishes You can apply two types of waterproof finish to flat roofs: 1. bituminous felt, which is a sheet material with a fibrous base soaked in bitumen. Felt is usually laid on timber roofs; 2. mastic asphalt, which is a material containing bitumen that is laid as a hot elastic covering. As it cools it hardens to form a jointless cover that is usually put on concrete roofs. Bituminous felt This roofing material is often called built up roof¬ ing because you put it on two or three layers deep as you can see in Figure 12.21. The felt is made from organic fibres like jute or synthetic material like fibreglass treated with bitumen to make it waterproof. The resulting flexible sheets are about 1 metre by 12 metres. Bituminous felt gives you the best results if you lay it very carefully around and under openings or projections such as outlets, verges, eaves and chimneys. In hot climates you apply a final treatment to the felt sheets that reflects as much light as possible so that the surface temperature is lower. This reduces the heat in the building and prolongs the life of the felt. Table 12.2 describes how to lay felt to provide the most efficient cover. 110 Building construction First layer of felt Timber decking to Layer of bitumen falls Second layer of felt Layer of bitumen Third layer of Layer of bitumen Chippings Bucket for the hot bitumen Roofing nail Figure 72.27 Laying a bituminous felt roof. Table 72.2 Laying bituminous felt Step Action 1 Roll out the first sheet of felt over the roof boarding and nail it with large head roofing nails. 2 Roll out the next sheet of felt so that it overlaps the first by 50 mm and nail it down. 3 Continue steps 1 and 2 until the entire roof is covered in a layer of felt. 4 Apply hot bitumen to the first layer of felt. Then roll out another layer, but do not nail it. The sheets in this layer should overlap the first layer by 50 mm. 5 Repeat step 4 with the third layer. 6 Spread a layer of white marble or limestone chips set in bitumen over the top layer to reflect heat. 1. outlets with raised edges that need to fit se¬ curely against the roofing felt; 2. abutments found on parapet walls. If the felt has to be laid vertically, then you can fix a wooden strip into the angle at 45° to avoid a 90° turn. The felt should stand 150 mm above the level of the roof with a cover flashing to prevent water entering; 3. penetrations where pipes pass through roofs. You can make a metal collar with a flat sheet to go under the felt and a cylinder to enclose the pipe. The felt should bond with the collar to make it watertight; 4. verges and eaves which need a drip, made of felt over a timber strip that protects the timber underneath. Figure 12.22 illustrates the details for junctions between flat roofs and openings. Mastic asphalt Working around openings and projections on the roof You need to lay the felt very carefully around: Mastic asphalt is usually applied to concrete flat roofs, but it can also be used on timber roofs. It is a mixture of graded limestone bonded with asphaltic cement to form a waterproof material that is plastic when heated. Roofs 111 Figure 12.22 Details of the junctions on a flat roof: (a) the upstand; (b) the verge; (c) the soil vent pipe; (d) the rainwater outlet. 112 Building construction (a) with wire mesh Figure 12.23 Roof ventilation: (a) ventilating a flat timber roof; (b) ventilating a pitched roof. 113 Roofs Table 12.3 explains how to apply a mastic as¬ phalt roofing finish. Table 12.3 Applying a mastic asphalt finish Step Action 1 Melt the solid blocks of asphalt in a boiler. 2 Sweep the roof surface. 3 Lay an underfelt cover over the roof surface that prevents the penetration of the asphalt into the roof surface. 4 Carry the hot melted asphalt in buckets to the roof. 5 Spread a 10 mm thick layer of asphalt by hand with a wood float. 6 Apply the second layer to the same thickness so that it melts into the first layer and welds the edges of the two layers together to a 20 mm thickness. 7 Make a 45° wedge at the junctions with vertical upstands that increase the thickness of the asphalt at weak points. Vertical upstands should be at least 150 mm above the finished level of the asphalt. 8 Spread a 12 mm layer of white crushed stone over the surface or paint the surface with reflective paint. Reflective finishes The reflective finishes that you read about in an earlier section are actually meant to protect the roof finish from the sun’s ultraviolet rays. In addi¬ tion, the light-coloured stones reflect the sun’s infrared rays and reduce the surface temperature. This reduces the amount of heat that can be trans¬ mitted into the interior of the building. Low-density materials Low-density insulation materials have air pockets that keep out the heat. Some of the common materials are: 1. expanded polystyrene boards made by bub¬ bling gas through polystyrene; 2. fibreglass mats, which are strands of glass loosely woven into a blanket to trap the air; 3. insulating fibreboard made from organic ma¬ terials, like wood fibre, that are loosely bonded to make a lightweight board. Most insulation materials work best if you put them under a bituminous felt or asphalt roof covering. The exception is the fibreglass mats, which would compress and lose the trapped air. The best method for using fibreglass mats is to cover the timber roof joists loosely before fixing the boarding. Wind effects on flat roofs Insulating a flat roof Heat enters the interior of a building by a transfer of radiation when the roof surface is exposed to the sun’s rays. You will notice this effect most under a corrugated metal roof if there is no ceiling. The transfer of heat can be resisted in three ways: 1. making the roof from materials with a high thermal resistance. This adds to the cost and weight of the roof; 2. putting in a ceiling that creates a roof cavity that traps heat until the air space in the cavity warms up. Ventilation slots in the eaves and the top of the gable ends can produce enough of an air movement to disperse the heat outside (Figure 12.23); 3. insulating the roof surface. A flat roof can be insulated by applying: • reflective finishes; • low density materials. Wind pressure can strip off tiles, lift overhanging eaves and verges and blow off corrugated sheets. If the roof covering is fixed very securely to the roof framework, then a strong wind could lift off the timbers of the roof structure. This can be prevented by using galvanised steel ties every 1800 mm. They should be taken across the wallplate and down the wall for 600 mm and embedded in a mortar joint. The ties can also be taken around the rafters to secure the roof struc¬ ture against the lifting action of wind. CHECK YOUR UNDERSTANDING 9 Roofs can be pitched or flat. • Pitched roofs are covered with tiles or sheet materials. @ Flat roofs are covered with asphalt or bitumi¬ nous felt. • Pitched roofs are constructed from timber. 114 Building construction # Flat roofs are constructed from timber or rein¬ forced concrete. The basic shape in pitched roof construction is the triangle. Roof trusses simplify the structure of a pitched roof. # Plain tiles are heavy and need more timber than interlocking tiles. # Flat roofs need a minimum slope to dispose of rainwater. # Flat roof finishes need protection from sunlight. 2 3 4 5 6 REVISION EXERCISES AND QUESTIONS 1 What are three functions of a roof? 7 Can you define these words: i) pitch ii) hip iii) gang nail plate iv) gauge v) parapet wall? Why does a flat roof need a slight slope? What are the functions of the structural mem¬ bers of a pitched roof? What is the difference between a roof truss and a trussed rafter? Draw the falls for a timber roof that spans six metres. How do you lay bituminous felt on a flat timber roof? Introduction Scaffolding is a temporary structure made from poles of wood or metal that lets you work on parts of buildings that you cannot reach from the ground. This chapter describes how to put up two different types of safe and secure scaffolding. The first use of scaffolding is for the external walls. When the brickwork is about shoulder high, then the bricklayer needs to be raised up to con¬ tinue working. Below 2 metres the scaffold boards can rest on timber trestles. This is a suitable work surface because the bricklayer can step up and down to get bricks and mortar. More than 2 metres from the ground, workers need ladders up to the platform, which must be wide enough to hold materials, plant and people. Platforms should be placed at 2 metre intervals as the height of the building increases, so that workers can comfortably reach their working area without hitting their heads as they walk under¬ neath. Bridles short lengths of tubing that are fitted to each side of a window opening and clamped to the transom. They fix the putlog scaffold to the surface of the building. Guard rails horizontal poles that are fixed above the working platform to stop workers falling off. Ledgers the horizontal poles that connect the standards. They are parallel to the building. Putlogs cross pieces that have one end built into the wall of the building. Reveal pins metal pins which tighten struts wedged vertically in window openings. Guard rail Platform -q Toe board r Bridle Technical words for parts of a scaffold Scaffolding uses many technical words such as those in this list to describe its parts. Base boards timber boards that support the base plate on soft or uneven ground. Base plates square metal plates that fit into the bottom of scaffold tubes to spread the load. Braces poles fixed diagonally to stiffen the scaffold by forming a triangle. Putlog Ledger Standard Base plate Figure 13.1 Parts of a putlog scaffold. 115 116 Building construction 2. the independent scaffold, which has a hori¬ zontal working platform that rests on vertical poles at both ends. See Figures 13.2 and 13-3 for examples of standard methods of construction for independent metal scaffolds. Scaffold poles are timber or tubular metal. The platforms are always made of timber boards which measure 225 x 2000 mm. Timber scaffolding has these advantages: 1. Trees are available to supply the poles. 2. It is usually cheaper to buy timber poles than metal. 3. The scaffold parts can be joined without special fittings. 4. The timber can be reused when not required for scaffolding. 5. It is easy to cut and fit. It also has disadvantages: 1. It takes longer to erect. 2. The pole joints are secured with string and nails rather than stronger purpose made fittings. 3. The timber may have hidden defects. 4. Timber putlog scaffold poles leave holes in the walls, to be filled in. Metal scaffolding has these advantages: 1. It is durable. 2. It is quick and simple to erect. 3. It is more adaptable. 4. The poles are all the same quality and strength. 5. Metal putlog scaffold poles have flattened ends which do not leave holes in the walls. The disadvantages of metal scaffolding are: Standards the vertical poles that carry the weight of the scaffolding to the ground. Toe boards the boards along the edges of plat¬ forms that prevent materials falling off. Transoms cross pieces that rest on the ledgers and support the platform. Types of scaffolding There are two types of safe scaffolding: 1. the putlog scaffold, which is supported at one end by the building under construction. One end of the working platform rests on the exter¬ nal wall and the other end is supported by vertical poles (See Figure 13-1); 1. The initial cost is higher than for timber. 2. The many joint fittings can easily be lost or stolen. 3. The poles must be carefully stored and pro¬ tected when not in use. Regulations and recommendations for scaffolding Regulations for the erection of scaffolding are very detailed because of the high risk of death or injury if scaffolding collapses. Safe working practices are essential. The regulations for scaffolding materials usually specify that: 117 Scaffolding 1. The poles and components must be in a sound condition and suitable for the purpose. 2. Metal poles must be free from rust. 3. Timber poles must not be split or contain any rot or insect holes. 4. Both metal and timber poles must be straight. 5. Poles should not be repaired or joined in ways that create weaknesses. 6. Poles must not be painted as this may conceal defects. The regulations for the safe erection of scaffold¬ ing normally state these principles: 1. The standards must be vertical or slightly in¬ clined towards the building. 2. The base of a standard must not rest directly on the ground or it could sink under pressure. The structure must have a base plate between the foot of the standard and the ground to take the load. 3. Putlogs and transoms that support the platform must be fixed securely to the standards or ledgers in an approved manner so that they do not move. 4. The scaffolding should be tied to the wall of the building under construction at 10 metre intervals across the building face. 5. Putlog scaffolding must have diagonal braces between the standards for the length of the scaffold. 6. Independent scaffolding must have diagonal braces between the standards on alternate bays. 7. The span between standards should be less than 2400 mm. 8. Scaffolds should be erected by fully trained people only. 9. Parts of the scaffolding should not be moved unless you check the changed fittings carefully. The working platform You should space the putlogs or transoms to suit the thickness of the scaffold boards as shown in Table 13.1. Table 13.1 Spacing ratios for putlogs and transoms Scaffold board thickness (mm) Putlog or transom spacing (metres) 32 1 38 1.5 50 2.5 118 Building construction The following list gives you some examples of standard regulations for a working platform. 1. 2. 3. 4. 5. The working platform must be at least 625 mm wide for walking. If the platform also holds materials, then it must be at least 900 mm. Where horizontal boards overlap, then you need to lay bevelled or shaped pieces of timber over the join to avoid tripping and to make it easier to wheel barrows. A board should not overhang the putlog or transom by more than four times its thickness. All platforms must have a guardrail that is less than 750 mm above the toe board. The toe board should be 150 mm high. The regulations about ladders state that they: # must be in good condition with no missing rungs; should be inclined at a 4:1 pitch; # must be at least 900 mm higher than the working platform; must be tied to a ledger at the top; # must stand on a level base at the bottom. CHECK YOUR UNDERSTANDING • A scaffold is a temporary timber or metal struc¬ ture that provides support for working platforms. • Working platforms are timber boards. They should be wide enough to hold workers and ma¬ terials. • Scaffolding must be strong enough to support people and materials. • Scaffolding should be attached to the building under construction at suitable points such as win¬ dow openings. Diagonal braces improve the stiffness of the scaffolding. • Good discipline is essential to prevent falling when working on scaffolding. • Part of the load is supported by the building in putlog scaffolds. The other part is supported by one row of standards. Independent scaffolds have a row of standards at each end to support the entire weight of the working platforms. • Make sure you know the rules for erecting, dismantling and using scaffolding, platforms and ladders. Inspection and maintenance As part of your good working practices you should carry out rigorous inspection and maintenance pro¬ cedures. You should check: 1. all parts of the scaffolding at least once a week and always after bad weather; 2. that all the uprights are vertical by sighting along the line of the standards; 3. that all the braces are in place and that the scaffolding is tied to the building; 4. that no important pieces were removed if the scaffolding has been partly dismantled; 5. that the guardrails and toe rails are supported and in place. REVISION EXERCISES AND QUESTIONS 1 2 3 4 5 6 What makes a scaffold stable? What are four different types of poles used to build a putlog scaffold? Draw the working platform on a putlog scaf¬ fold. Draw an independent scaffold. How do diagonal braces stiffen scaffolding? What are three advantages and disadvantages of these types of scaffolding: i) timber ii) metal? Stairs Introduction Buildings have stairs so that people can gain ac¬ cess to the upper floors. Stairs should be designed so that they are convenient for the majority of people to use. Because the very young or very old may find it difficult to go up and down stairs safely you should put sturdy handrails within reach. The handrails should be supported by balustrades on the open sides of staircases to prevent accidents. This chapter tells you how to design, assemble and build simple staircases. Technical words for parts of staircases This section defines the words for the main parts of staircases. Figure 14.1 illustrates many of the im¬ portant parts of timber, concrete and steel staircase structures. Baluster the infill between the handrail and the string. It usually consists of square vertical balus¬ ters fitted to the string capping and supporting a timber handrail. For safety reasons, the gaps be¬ tween the uprights on the balustrade must be less than 100 mm apart. It can also be wide rails that run parallel to the string with a handrail supported by intermediate balusters. These balusters can be spaced more widely. Balustrade the protection erected on the outer edge of a staircase to prevent anything or anyone falling off the edge. Flight a series of steps between floors or a floor and a landing. Going the horizontal distance between two adja¬ cent risers. Handrail an inclined rail that follows the slope of the stairs, which is either fixed to a wall or supported on a balustrade. Landing the level space that breaks up the ver¬ tical incline of a flight of stairs. Newel a stout vertical post at one end of the outer string. Its function is to support the inclined handrail at each end. Newel post the main support for the handrail for a timber staircase. Nosing the part of the tread that projects beyond the face of the riser. Rise the vertical distance between the tops of adjacent treads. Riser the vertical surface of a step. String the side support for a flight of timber steps. The strings are two timber pieces that form the sides of a staircase, which measure about 38 x 250 mm. The treads and risers are usually fixed into the strings in 12 mm slots, which are tapered to take wedges. Tread the horizontal surface of a step where you place your feet. The treads in a timber staircase are made from solid timber that is about 25 mm thick. The risers are usually solid timber about 19 mm thick or 12 mm plywood. The treads are attached to the strings and joined to each other. Staircase materials You can build staircases out of timber, reinforced concrete, steel or stone. Timber staircases are the most traditional. A timber staircase usually consists of two strings, treads and risers, a balustrade and a handrail (Fig¬ ure 14.1). 120 Building construction Handrail (d) Steel handrail and balusters bolted to Figure 14.1 The construction of timber, concrete and steel staircases: (a) parts of a staircase: an overview; (b) parts of a timber staircase; (c) parts of a concrete staircase; (d) parts of a steel staircase. 121 Stairs Reinforced concrete staircases are increas¬ ingly popular. They are usually cast in situ on formwork. The treads and risers are cast in one piece so they do not have strings. Steel staircases are normally used for fire escapes or for external access. A typical rnetal staircase has metal strings with steel treads fixed to metal brackets. Steel staircases usually do not have risers. Stone staircases are rare. The parts of staircases can be made from differ¬ ent materials. Balustrades are usually timber in timber staircases, but could be timber or metal for concrete stairs. Metal staircases usually have steel balustrades. Staircase layout A straight flight of stairs is the most simple layout. (Figure 14.2.) If the flight changes direction be¬ tween levels, then you need to provide a landing. The degree of change in direction determines the size of the landing: Figure 14.2 Standard staircase layouts: (a) straight flight of stairs; (b) 90° turn with a quarter landing; (c) 180° turn with a half landing; (d) tapered staircase with no landing; (e) dog-leg staircase. 122 Building construction 1. A 90° turn needs a quarter-space landing. 2. A 180° turn needs a half-space landing. You can put the landing in any position on the flight of stairs. A landing at the top of the flight leaves enough room for an understair cupboard below. Tapering the steps is another method of chang¬ ing direction. Tapered steps do not need a landing and use less space, but are more dangerous to use because the reduction in the inner edge makes walking difficult. A staircase that turns through 180° can either have a well or a dog leg. The dog leg uses less space since the two outer strings sit over one another. Formula for calculating stair dimensions The going plus the height of two risers must be: maximum of 700 mm; Q minimum of 550 mm. To ensure that stairs are not steeper than 42° the relationship between the riser and the going must be based on the measurements in Table 14.1. Table 14.1 Riser and going dimensions Riser (mm) Going (mm) 155-220 245-260 165-200 220-305 General principles of staircase design The first principle in staircase design is that a person should be able to move comfortably from one step to another (Figure 14.3). The design must conform to the typical step pattern of an average person. As the going increases, then the riser height decreases. The reverse is also true. Increased riser height means a decreased tread length. The goal is to find the compromise between tread length and riser height using a standard formula. Each riser in a flight of stairs must be the same height. Each tread must be the same length. The total number of risers depends on the height of the vertical rise of each flight. Designing a straight flight of stairs This section describes how to design a straight flight of stairs using a standard formula. The dimensions for the staircase are: vertical rise = 2760 mm staircase length = 3000 mm preferred riser height =190 mm Using this information Table 14.2 shows you how to calculate the number of risers and treads to find out the length of the staircase. This informa¬ tion is also shown graphically in Figure 14.4. Assembling a timber staircase Figure 14.3 An example of a comfortable relation¬ ship between horizontal and vertical movement. The timber pieces for a staircase can be cut to size from full-size templates prepared from the dimen¬ sions on the working drawings. You use machines to make the grooves, mouldings and housings that join the pieces of the staircase. The entire structure can be assembled off site and transported to the building intact. Table 14.3 describes how to put a timber stair¬ case together from the timber pieces. Figure 14.5 is a view from below of the assembly of a timber staircase. Stairs Figure 74.4 Designing a staircase: calculating the number of treads and risers. 123 124 Building construction Table 14.2 Calculating the length of the Table 14.3 Assembling the staircase staircase Step Action Step Action 1 Glue the treads and risers. 1 Divide the vertical rise by the riser height to find the number of risers: 2760/190 = 14.52 risers Try 14 risers. 2 2 Find the exact riser height by dividing the vertical rise by the number of risers: 2760/14 = 197.14 Insert the treads and risers in the grooves in the strings. Lightly nail them together. Insert and glue two wedges in each tread to strengthen the joint. Press the structure together with a cramp iron. 3 3 Find the going to suit the desired staircase length: 3000/13 = 231 4 Use the formula 1 tread + 2 risers to see if this design is comfortable: 231 + (197.14 x 2) = 625.28 If the staircase is more than 1 metre wide, then add a support called a carriage fixed to the floor at each end: this is a piece of timber with brackets fixed on alternate sides to support the middle of each tread. 4 Fix a 75 x 75 mm newel post at the top and bottom of both strings. Make a slot in all the newel posts for the strings and adjacent treads and risers. Make a small slot in the upper newel post to fit the first floor trimmer joist. 5 Glue and screw all the parts of the staircase together. 6 Fit the handrail in position about 850 mm above the slope of the tread nosings and insert it into the newel posts. 7 Insert the balusters into the handrail and the string at less than 100 mm intervals. 8 Transport it to the site and put the complete staircase into the building. 5 Does the design come within the allowable limits? Check against Table 14.1. 6 If YES, use staircase with 14 risers: 231 mm going and 197.14 mm riser 7 If NO, repeat from step 2 with 15 risers. If this still doesn't fit increase the staircase length and repeat from step 3. Fixing a timber staircase on site You fix the string to the wall with plugs and screws. It should fit tightly against the staircase trimmer joist at the top and be cut and shaped to fit against the skirting beside it. The lower end of the staircase rests on the floor. Again, cut and match to the skirting as required. Insert the outer string in the newel posts at the top and bottom. The stairwell trimmer slots into the top newel post and they are screwed or nailed together. Fix the lower newel post to the floor with brackets. Finally, fit the handrail and balustrade to the string and newels to complete the staircase fixing on site. A reinforced concrete staircase is a slab that spans between two different floor levels. The mini¬ mum thickness of the slab where the riser and tread meet must be at least 150 mm. Since the slab is cast on a smooth inclined deck, the underside of the finished staircase should be smooth and unbroken. Building the formwork (Figure 14.6) You follow these steps to build the formwork for the slab: Making a concrete staircase A concrete staircase is usually made on site. The construction procedures are the same as for other concrete slabs: 1. Erect timber formwork. 2. Position the steel reinforcement. 3. Pour and cure the concrete. 1. Cut out an outer string shaped like the treads and risers from a single piece of timber. 2. Place it in position on site. 3. Build the deck and support it with joists and props. 4. Fit the outer string to the deck. 5. Fix the structure into a secure position. 6. Fix the formwork for the risers in position so that they are supported above the deck. 125 Stairs Batten Hangers Riser formers Joists Figure 14.6 Constructing concrete stairs: (a) placing the formwork for concrete stairs; (b) suspending the riser formers from hangers; (c) placing reinforcement for a flight of stairs. 126 Building construction Figure 14.7 Two types of baluster for stair balustrades: (a) vertical balusters; (b) inclined balusters. 127 Stairs 7. Use hangers suspended from a batten fixed to the wall on the inner side and fix the riser form to the cut string on the outer side as you can see in Figure 14.6. 8. Treat the formwork with oil so that it can be easily removed when the concrete hardens. Placing the reinforcement Your next job is to place the reinforcement in the formwork. The main reinforcement must run from top to bottom in the slab. Put the main reinforce¬ ment on the sloping deck of the formwork using 25 mm spacers to keep it off the bottom. Link the reinforcement bar at the top to the starter bars that project from the first-floor concrete slab. (Refer to Chapter 11 on floors for more informa¬ tion.) Wire cross reinforcement bars across the main reinforcement bar at each step. Placing the concrete Make a stiff 1:2:4 concrete mix. The water to cement ratio should be as low as possible so that the mixture is not so wet that it flows downhill on the slope. Beginning at the bottom step, pack the concrete into the formwork. Vibrate it and finish it off smoothly with a trowel. Repeat these procedures for each step until you reach the top. You may need to use a platform to reach the upper steps until you can work from the first-floor slab. Cure the concrete and remove the formwork after 14 days. Handrails and balusters for concrete staircases Concrete staircases usually have steel balusters. They are fitted into holes made in the treads and fixed with mortar or bolted to the sides of the concrete. The handrail can be metal or timber. Figure 14.7 shows you balusters with vertical and sloping rails. The handrail and balusters can be many differ¬ ent designs. You should take note of designs that you see elsewhere. Whatever design you use, you must make sure that the handrail is at the correct height and that the space between the handrail and steps is filled in safely to prevent accidents. Figure 14.8 is a section to show you how a baluster should be fixed to a handrail and staircase. CHECK YOUR UNDERSTANDING A staircase provides access to different floor levels. The staircase should be comfortable for the average person to use. A staircase should have a slope less than 42°. 128 Building construction The length of the treads or the height of the riser can be adjusted to find the best slope. A formula for a comfortably designed staircase is T tread length + 2 risers height = 550-700 mm’ • All treads must be the same height in a flight of stairs. • All risers must be the same height in a flight of stairs. 9 Stairs can be made from timber, concrete or steel. • Timber and metal stairs are usually made off site. 9 Concrete stairs are usually made in situ. 9 A reinforced concrete staircase is a slab that spans the floor levels. 9 Balustrades should be spaced less than 100 mm apart. 9 Handrails should be about 850 mm above the slope of the nosings. REVISION EXERCISES AND QUESTIONS 1 2 3 4 5 How steeply can a staircase rise if the tread is 225 mm? Draw the fixing of a metal baluster to a con¬ crete stair. Draw a section of a timber staircase to show how treads and risers are fastened to a string. Draw a flight of five concrete steps with a landing. Show the formwork and reinforce¬ ment. ' Draw the following layouts for a one metre wide staircase with sixteen treads: i) a dogleg staircase with two equal flights ii) a staircase that winds around three sides of a stairwell with flights of six, four and six treads iii) a staircase with a quarter-space landing and two equal flights. Introduction A door is a movable barrier that separates internal and external spaces. It is usually attached to a frame on one side by hinges. A door provides access, protection, security and privacy. This chap¬ ter describes how doors are made and how to build them into wall openings. Ironmongery is an important part of door furni¬ ture. You can also read about the main types of ironmongery and how to fix them to doors and their frames. constructed to high specifications and fitted with high-security locks. Fire-resistance Internal doors that separate spaces are usually made of materials that prevent the rapid spread of fire. They are also heavy enough to be self-closing. Sound insulation Heavier doors provide better sound insulation. Privacy Solid doors are the most private. If some light is needed while retaining privacy, then obscure glass should be fitted. Performance standards A door, depending on the type, should meet cer¬ tain standards for: 9 weather resistance; • security; fire resistance; 9 sound insulation; • privacy; 9 operation; • durability. Weather-resistance External doors need a minimum gap of 2 mm for free movement. This gap should be sealed with suitable draught and water excluders to make the doors weather-resistant. Security The security of a door depends on the materials used, the quality of the frame and the ironmon¬ gery. Internal doors only need to provide minimal security. For example, a bathroom door might be fitted with a simple lock. External doors need to be Operation Doors can swing or slide open and closed. Most doors swing on hinges fixed to door frames. Springloaded latches usually hold doors closed. You normally open doors with knobs or levers. Durability Doors are in constant use. Their construction should be strong enough to withstand considerable activ¬ ity. A door should not fall off the edge fixed to a frame under its own weight. External doors should be able to resist climatic extremes, which can cause the shape to warp. Technical words for parts of a door This section defines the main parts of a door. So that you can see what they look like, the parts are also labelled in Figure 15.1. 129 130 Building construction Cill a horizontal member at the base of an exter¬ nal door that separates the internal and external structure. It should slope so that rainwater flows outside rather than inside. Frame a solid timber or metal structure fixed to a wall. It is constructed so that it forms a seal when the door closes and supports the door’s weight. Head the horizontal piece at the top of the frame. Jamb the vertical part of the frame that is fixed to the wall. Lining the timber framework inserted into an opening in an internal wall. Rebate a recess in the door frame that seals the edges of a door. Stile the outer vertical piece of the door frame. There are three types of stile: 6 hanging stile that the door hangs on; closing stile that holds the lock or latch; meeting stile where a pair of doors meets in the middle. Stop a thin piece of timber fixed to the head and jambs of the lining to form a rebate. Threshold the access point in the doorway where you enter or exit. The cill is part of the threshold. Water bar a metal bar fitted into the cill of an external door to prevent water flowing inside. Weatherboard a horizontal piece fixed to the external bottom edge of a door to push water away from the cill. Door construction You can make doors out of these different struc¬ tural pieces: 1. ledges, braces and battens; 2. frames, ledges, braces and battens. Frame (Jamb) 131 Doors Making a ledged, braced and battened door This is a very simple door for internal or external use, which is cheap to make. For an illustration look at Figure 15.2. It consists of these pieces: tongued, grooved and V-jointed battens measur¬ ing about 100 x 10 mm that form the surface of the door. The joints should be vertical; horizontal pieces called ledges measuring about 100 x 25 mm; diagonal pieces called braces that measure about 100 x 25 mm. Braces should be fixed so that they slope up away from the hinges. You follow these steps to construct this type of door: 1. Assemble the battens so that they are the right size for the door. 2. Glue the tongues and grooves together. 3. Screw or nail the battens to the ledges. 4. Cut out and fit the braces between the ledges. 5. Nail the battens to the braces. This type of door does not have any special woodworking joints. Making a framed, braced and battened door This door is stronger than the ledged, braced and battened door because the battens are set inside a timber frame (Figure 15.3). The framed, braced and battened door consists of these pieces: battens that form the surface of the door; a frame with a head rail, bottom rail and two stiles; a ledge; • braces. Head Figure 15.2 An example of a ledged, braced and battened door. Figure 15.3 An example of a framed, braced and battened door. 132 Building construction Figure 15.4 The construction of standard flush doors: (a) standard flush door; (b) a frame for a standard flush door; (c) facing and edging for a flush door; (d) an alternative core using a cardboard lattice. 133 Doors The basic steps for constructing this type of door are to: 1. Cut and assemble the pieces of the frame to fit the door size. 2. Insert the head and bottom rails into recesses in the stiles. 3. Fit the braces. 4. Nail the battens on the braces and stile. You can construct battened doors using dif¬ ferent methods. • You can omit the braces, but the door may drop because it is not rigid enough and lose its shape. • You can put the bottom rail of the frame behind the battens so that the door is only framed at the top and sides. Flush doors Flush doors have no projections or recesses on either surface of the door. These doors are usually made of large sheets of plywood or hardboard. Flush doors may have glazed panels to allow in some light. The construction of flush doors is shown in Figure 15.4. This list describes the parts that are specific to a flush door: A core is the inner part of the door. The external boards or sheets of plywood are fixed to it. The core can be made from: 1. a softwood framework of horizontal and vertical pieces joined together in recessed joints; 2. a cellular centre of paper or cardboard strips glued together in a lattice pattern; 3. a solid centre of timber strips glued together. This type of core makes a very heavy door with good sound insulation that can be used for external doors and fire doors. A flush panel is 3 mm plywood or hardboard sheets which are fixed onto the core material. A lipping is a thin wooden strip that protects the edges of a flush door panel. A lock block is a piece fitted into the internal framework of the door to make the recess for the lock. Flush doors are usually made in factories. This ensures a high-quality, durable product if the cor¬ rect type of door is put in the right location. The plywood facing and the frames for external flush doors should be fixed with waterproof glue. Panelled doors Panelled doors are suitable for internal and exter¬ nal use. They are made from solid timber frames with solid or glazed panels. This list describes the main parts of a panelled door not defined in earlier sections: Intermediate rails are cross pieces that divide the door into panels horizontally. Muntins are the central vertical pieces. Bottom rail is the bottom horizontal framing piece. Panels are the filling between the framing pieces. They can be: • thin, solid timber; • 6 mm plywood; • clear or obscure glass. You can see what the parts of the door look like in Figure 15.5. 134 (a) Building construction Counter-sunk hole P- N Counter-sunk screw Doors The panels are usually fitted into rebates in the frames and screwed or nailed into place. This method allows you to remove and replace panels, including glass panels, easily when required. Ironmongery Basic door ironmongery consists of hinges, locks and latches, which are illustrated in Figures 15.6 and 15.7. Doors swing open and shut on their hinges, which are the points on which doors move. Strap hinges are mainly used with ledged, braced and battened doors. These 150-600 mm hinges are made from wrought iron or pressed steel. Butt hinges are found on most internal and external doors. They come in a variety of materials and sizes including: 1. steel, which is used for all internal flush doors. A steel butt hinge is pressed and bent to form a knuckle for a pin to pass through; 2. brass, which is used on external doors if rust is likely to be a problem. Brass hinges look like steel hinges, but brass is more attractive on polished hardwood doors; 3. wrought iron, which is usually specially de¬ signed for external doors. The structure of a butt hinge consists of two separate leaves held together by a pin. The pivotal part of each leaf interlocks with the other leaf. As the door moves, the two pivoting parts of the leaves press against each other. Butt hinges are fixed to the door or frame with countersunk holes to take flush fitting screws. Most butt hinges are about 100 x 25 mm. Each door has two or three hinges fixed so that the leaves are flush with the surface of the door and frame. Locks and latches A latch, which is a door catch lifted by a lever, is fitted to a recess in a door. When you release the handle to close a door, then a spring pushes the latch bolt out so that it projects from the edge. The end of the latch bolt, which is curved on the surface, rides over a metal plate and springs back into the recess in the door frame. A door lock secures a room or building. Once 135 the lock is engaged in the recess of the frame you can only open it with a key. The bolt of a lock is square and not spring-loaded. Lock and latch combination are often inserted into one case to put in the recess in a door. A night latch combines a lock and latch into one unit with one bolt. The bolt is curved so that you can shut the door by pushing or pulling it closed. When the door is closed, then you must have a key to open it from the outside. You can just turn the handle to open it from the inside. Methods of fixing locks and latches Locks and latches can be rim fixed or morticed. A rim lock or latch is fixed on the internal surface of a door. The lock mechanism is contained in a steel or brass box. Night latches are often rim fixed. The locks and latches fitted to ledged, braced and battened doors are also usually rim fixed. Morticed locks and latches are set in a recess, called a mortice, that is cut into the edge of the door. Most deadlocks and lock and latch sets are morticed. All that you can see is the faceplate of the lock and latch assembly on the edge of the door. Other door fittings Doors also have handles and bolts. The handles are knobs or lever handles that operate latches. They are screwed to the surface of the door. Square spindles that pass through the latches fit into sockets in the bases of the handles. Security bolts are often fitted to the inside of an external door as an additional safety measure against intruders. Another type of bolt is fitted on double doors to hold them in closed positions. Door dimensions Doors for domestic buildings are usually about 2 metres high. Their width varies, as shown in Table 15.1. Table 15.1 Door dimensions Type of door Thickness (mm) Width (mm) External door 40-50 760-900 Internal doors 40 680-760 Fire-resistant doors 44 760-900 136 Building construction (b) (a) (C) (d) Spindle hole Mortice recess in the edge of the door Key hole Figure 15.7 Examples of standard door locks and handles: (a) lever handle; (b) door bolt; (c) pull handle; (d) recessed mortice lock; (e) rim lock. 137 Doors Door frames and linings The purpose of door frames and linings is to: 1. define openings; 2. reduce the gap between a door and a wall; 3. provide fixings for the hinges and a recess for the lock or latch; 4. provide a finish between the door and the wall. Door frames are usually made from solid timber with a rebate to house the door. The frame is not related to the thickness of the wall surrounding it. A typical timber frame for a 50 mm external door could be 125 x 75 mm with a 12 mm rebate. Door linings are usually fitted to internal doors where the lining is the full width of the internal wall. A timber stop nailed to the lining provides a rebate for the door to close against. Fixing door frames and linings You should follow these steps to fix a frame or lining into place as the wall is built: 1. Brace the frame or lining to keep it square. 2. Paint the back of the frame to prevent the entry of moisture from the masonry. 3. Screw galvanised metal fastenings to the back of the frame or lining which match the masonry courses. 4. Stand the structure in position, level and support it with struts. 5. Build the fastenings into the masonry joints to secure the frame or lining in position perma¬ nently. You should follow these steps to fix a frame or lining into the wall after the wall is built: 1. Leave an opening that is about 3-4 mm bigger than the frame when the wall is built. 2. Insert wood plugs into some of the masonry joints that face the opening during construction. 3. Put the frame in position after the wall and lintel are built. 4. Level the frame with small timber pieces. 5. Drill holes in the frame or lining for screws to go into the plugs in the masonry. 6. Countersink the screws and fill the holes. CHECK YOUR UNDERSTANDING Doors are a means of securing access to rooms and buildings. Doors must resist fire and weather and provide security. They swing on hinges on one side and close into a frame on the other. Doors are usually timber. Door panels may be glazed. Flush doors are made of hardboard or plywood. Doors made from solid timber usually have panels. Solid doors can be made from tongue and groove battens on timber frames. Frames and linings finish off the gap between doors and walls. Most ironmongery is standard and manufactured to suit the various requirements for hinges and locks. REVISION EXERCISES AND QUESTIONS 1 2 3 4 5 Draw the structure of a framed, ledged and braced door with left-hand hinges. What are two methods for fixing glass into panels? Draw a standard flush door. What are two methods of fixing locks and latches? Draw a threshold of an external door. Introduction Windows provide natural light and ventilation to the interior of a building while excluding rain and insects. The glass in the windows must be strong enough to resist wind pressure. This means that the thickness of the glass increases as the size of the glass pane increases. Windows are usually made of timber or steel, but other materials such as plastic or aluminium are also popular. This chapter describes some of the most common types of window and their standard measurements. Since windows provide a point of entry into a building, they may need locks or burglar bars for security. This chapter also looks at how to fix security screens and grilles to standard win¬ dows. Head Transom Mullion Jamb Top rail Cill Stile The parts of the fixed frame The parts of the moving sash Bottom rail Figure 16.1 The parts of a window. 138 139 Windows Technical words for parts of a window and frame The technical words that describe the main parts of windows and frames are in the following list. Figure 16.1 shows you what some of the main pieces look like. Bottom rail the bottom member of a sash or light. Head the top piece of a window, which is fixed to the underside of the masonry. Casement a side-hung opening window. Cill the bottom piece of a window, which is fixed to the bottom of the opening. Jamb the vertical sidepiece fixed to the surface of the window opening. Mullion a fixed vertical piece in the window framework, which separates the fixed and moving parts. Opening light another word for a sash. Sash the whole moving part of a window includ¬ ing the glass. Stile the side member of a sash. Top rail the top member of a sash. Transom the fixed horizontal piece that sepa¬ rates the fixed and moving parts of the window. Ventilator a small sash, which is often top-hung to provide secure ventilation. Types of window Standard windows can have four different types of opening section as you can see in Figure 16.2: 1. Side-hung windows have hinges on one side and the fastening catch and handle on the other. 2. Top-hung windows have hinges at the top and a securing stay at the bottom. This window opens out. 3. Bottom-hung windows have hinges at the bottom and a securing catch at the top. This window opens in and needs a special stay to stop it falling into the room. 4. Louvres are individual pieces of glass held in clips and opened by a lever arm, which locks the louvres in position. The top- and bottom-hung windows are useful when ventilation is required, but the room must be secured against rain or intruders. If you want to control the flow of air you need a type of window that increases or decreases the size of the opening. This can be a: glazed and hinged sash; solid battened timber sash without glass, which excludes daylight and ventilation when it is shut. It is normal for part of a window to be fixed. This part, which has the glass fixed directly to the framework of the window, is called a fixed light. Ironmongery for an opening sash Building regulations for windows Windows are usually put together in combinations of opening and fixed lights to comply with the regulations for health and hygiene in habitable rooms. Habitable rooms must have adequate fresh air and light in rooms used for living, eating and sleeping. The standard requirements in most build¬ ing regulations are usually: 1. The minimum area of window in a habitable room should be 10 per cent of the floor area. 2. The minimum opening area of the window in a habitable room should be 5 per cent of the floor area. Sometimes permanent ventilation is required in a room. You can put in a mesh-covered opening in the head of the frame to keep out insects and to provide air. The ironmongery for an opening sash consists of: 1. hinges, which are screwed to the timber pieces. The hinges are usually riveted to steel frames; 2. casement fasteners, which are fitted on the opposite sides of the hinges on side-hung win¬ dows. They keep the window closed; 3. casement stays, which are metal arms with holes along their length fixed to pivots on the bottom pieces of the sash. They hold the tophung and side-hung lights in the open position. Window height Windows may be custom made or standard. Cus¬ tom made means that the window is designed for a specific building. Standard means that a manu¬ facturer produces a range of windows to fit typical 140 Building construction Side-hung casement Figure 16.2 Different opening lights. window openings. It is cheaper for a building designer to design openings to fit standard windows. Window dimensions are usually related to nor¬ mal brick dimensions. The height should suit a 75 mm brick course. The most practical height ranges from 300 to 1500 mm. To make a taller window, you can introduce an extra horizontal bar to join windows if they are made from steel. Window heights are usually increased in incre¬ ments of 300 mm. If you build a door into the window design, then the structure has an overall height of 2100 or 2400 mm. The height is usually determined by the size of the lintel. Other factors that influence the height are: 1. the requirement for security. Small windows are more secure; 2. heat gain. Heat from surrounding surfaces enters through a window; 3. glare. The intensity of the light entering from outside may need to be restricted; 4. handling. The practicalities of lifting and trans¬ porting window units may determine the best size. The actual size of a window is slightly smaller than the dimensions given here, to allow for fixing and bedding. Example A window opening that measures 1500 mm vertically will require a window that is 1490 mm to allow for 5 mm bedding on top and bottom. Combination windows The height of a window with a moving part should be less than 900 mm or the glass will be too heavy and subject to distortion from strong winds. Al¬ though the total height can be up to 2400 mm, the vertical sash should be divided into panels. A convenient width for a moving part such as a casement is 600 mm. Wider units usually have a mullion fitted. If a 600 mrn^casement is part of a window unit with a 600 mm fixed light, then the overall width of the window is 1200 mm. Table 16.1 shows you typical incremental in¬ creases in width for combination windows. 141 Windows Table 16.1 Combination window widths Window combination Width (mm) One casement 600 One casement and one fixed light 1200 One casement and one 900 mm fixed light 1500 Two casements and one 600 mm fixed light 1800 Two casements and one 900 mm fixed light 2100 Two casements and one 1200 fixed light 2400 Louvred windows A louvred window is a window with rows of sloping blades of timber or glass called louvres fitted into a frame. You fit this assembly into an opening so that the louvres slope out and down to deflect rainwater, but still allow the air to flow in and out freely. Louvred windows may need an insect screen to keep insects and leaves from blow¬ ing in when the louvres are open. Louvres can be fixed in position or slotted into pivoting clips on each side of the frame. The clips are tilted by an operating arm which opens, closes and locks the louvres. Louvred windows usually need burglar bars fit¬ ted behind the glass since the louvres can easily be removed for entry into the building. Glazing The glazing is the glass part of the window. Glass is essential to let in daylight, but to exclude wind and rain. The thickness of a pane of glass depends on its height, width and amount of likely wind pressure. These types of glass are commonly used in small buildings: 1. clear glass, which is about 3 to 4 mm thick; 2. obscure glass, which is used in private areas such as toilets and bathrooms. It is usually about 4 mm thick and comes in a variety of patterns; 3. special glass, which is used in internal or exter¬ nal doors that require stronger safety glass. Figure 16.3 Two methods for fixing glass in timber frames. 142 Building construction Mastic pointing Drip moulding Capillary grooves Bottom rail Capillary grooves Transom Mastic pointing Fixing screw Capillary grooves Figure 16.4 Detailing timber windows. Filler or wood plug Plug in wall 143 Windows There are two main types of special glass: wired glass, which can be clear or obscure. It is about 6 mm thick and is reinforced with wire; toughened glass, which is manufactured to a specific size and cannot be cut. When this glass breaks it shatters into harmless pieces. Car wind¬ screens are made from toughened glass. Head and top rail joint Make a groove in the head and the rail to form a gap to prevent water spreading across the joint. Bottom rail and transom joint Make a groove and put a drip mould in the bottom rail to prevent water spreading across the joint. The bottom edge of the rail and the top of the transom should slope to meet each other. Fixing glass in frames (Figure 16.3) The method that you use to fix glass in frames depends on whether the frame is wood or metal. Follow these steps to fix glass in wood frames: 1. Prime the wood to keep the oil in the linseed putty. 2. Apply putty to the recess in the frame and fit the glass. 3- Put more putty around the outside of the joint where the glass lies in the frame. 4. Level off the putty so that it slopes to line up with the top of the recess (creating a sight line). 5. If the glass is fixed to an internal door, then bed the glazing in timber glazing beads, which are nailed to the frame on four sides. This prevents the glass rattling when the door is opened and closed. cm Make a groove in the underside of the cill where it projects past the masonry to prevent water running back under the cill. Cm masonry joint Fill the joint between the cill and the masonry with mastic. Jamb of frame Point this joint with mastic. Jamb and stile joint Make grooves. Stile and mullion joint Make grooves. Follow these steps to fix glass in steel frames: 1. Use a special metal glazing putty, which sticks better than ordinary putty. 2. Put the bottom edge of the glass on two small blocks so that it does not rest on the metal. 3- Continue fixing as for wood frames. Excluding water from timber windows Timber windows need to be designed so that water does not enter. This section describes what to do to each part of a timber window to prevent this. See Figure 16.4 for the specific detailing re¬ quired. Using metal windows Metal windows are usually made in factories of Z-section steel, which forms the frame and moving parts. They can be ready-made units or custom built to specific dimensions. Metal has these advan¬ tages over timber windows: 1. The metal sections are smaller, which increases the area of the glazing. 2. They are not subject to rot or insect attack (but they may rust near the sea). 3. They are easier to make. Figure 16.5 shows you how metal windows are fixed into concrete cills and lintels. Head Point the joint between the head of the frame and the lintel or arch with a non-setting mastic, which remains intact even if the frame shrinks a little. Making window cills Top rail Put a drip moulding on the head of the frame to deflect water from an opening sash. You can make window cills in timber, brick, tile or concrete. Each of these materials must achieve the same results: 144 Building construction Concrete lintel . t -o; .ao $ i • * 0 .0. . Fixing screw in a plug in concrete Fixed frame Transom Side-hung casement Precast concrete cill ■' c7O 0 Figure 16.5 Parts of a metal window. 1. The cill must project past the surface of the wall by 50 mm so that the water running down the surface of the window clears the wall. 2. It must be designed so that water runs off and not back to the wall along the underside. 3. It must have enough slope on its upper surface to discharge rainwater. 4. The bottom window frame must be slotted in so that water cannot enter. Fixing windows to openings A timber window can be fixed in place as an opening is built or afterwards. Generally, it is better practice to fix the windows later to prevent exposure of the internal parts to the weather. To do this, you must fix plugs into the recesses in the frames and the cill during construction and then screw the windows in place. 145 Windows You follow the same procedure to fix windows in place while the walls are being built as you do for doors. See Chapter 15. Metal windows are usually fixed in place after the walls are constructed. You should leave holes in the frames for screws to fit into the plugs in the walls. After the frame is inserted, you should fill the joint around the frame with a waterproof mas¬ tic cement. Figure 16.6 illustrates the correct detail¬ ing for a metal window embedded in a precast concrete cill. Keeping out intruders and insects You will need to consider security and the exclu¬ sion of insects like mosquitoes in the window specification. An open window at ground-floor level is almost an invitation to someone to enter a building. If the glass can be lifted out easily or broken, then you may need to fix metal grilles inside the window. These grilles, often called burglar bars, are made from 6 mm steel bars welded together in a strong and decorative pattern. The grilles should have access holes large enough for you to put your hand in to operate the window fittings. Figure 16.7 shows you an example of a decorative pattern for burglar bars. Internal timber cill Figure 16.6 Metal window on a precast concrete cill. Insects usually have a daily and seasonal pat¬ tern. Since wire screens to exclude insects reduce daylight and obscure the view, it is useful to have temporary mesh panels that can be inserted when needed. If the building also has security grilles, then the mesh screens need to be inside the grilles, for removal or they must be hinged. Fixing grilles and screens Security grilles must have projections on each side to slot into the side of the window opening. They also must be small enough so that the plasterer can work on the opening reveals. Insect screens can be hinged on frames which are fixed flush with the inside walls so that they fold back when not in use. Removable screens need safe storage space so that the mesh is not damaged. CHECK YOUR UNDERSTANDING # Windows provide light and ventilation to the interior of a building. 6 Windows have glass to admit light while exclud¬ ing the weather and insects. # Windows may have security grilles and insect screens for added protection when they are open. # The main structure of a window is the fixed frame and movable sash. # Sashes can be hinged to a frame in different ways. 146 Building construction © Windows can be timber, steel, plastic or alu¬ minium. Building regulations usually specify the mini¬ mum sizes of windows and their opening parts. © Windows can be custom made or standard. • Glazing can be clear or obscure. © Glass can be fixed in the frames with putty or wooden beads. © Windows must be carefully designed and con¬ structed to exclude water. © Louvres are timber or glass strips which are movable to allow ventilation. REVISION EXERCISES AND QUESTIONS 1 2 3 4 5 What ironmongery do you need for a sidehung window? What size manufactured window do you need for an opening that is 1200 x 1500 mm? How do you ensure that water does not enter timber windows? What is the purpose of a cill? What are three ways that metal windows are better than timber? Figure 16.7 A decorative security grille on opening lights. •v Introduction The design of a building needs to include provi¬ sion for drainage. In a domestic building, facilities are required for: 1. personal washing; _ 2. disposal of human waste products; 3- preparing food and washing kitchen utensils. All these activities use water, which must be supplied to the building. After its use, the waste water must be disposed of so that it does not pollute the environment or cause a health risk to the occupants. Figure 17.1 gives you an overview of the route that the waste water for these activities takes from a building to a public sewer. Water that contains human and domestic waste is called effluent or sewage. It should be col¬ lected from the building and drained into a system of pipes and sewers that ends at a sewage treat¬ ment plant or sewage disposal works. When the sewage is treated, then it can be returned to the sea or rivers in a clean condition. If there is no system of public sewers, then you need to supply an independent system for collect¬ ing and treating sewage, such as a septic tank or cesspool. The main difference between a cesspool and a septic tank is that a cesspool does not break down and treat the sewage. The cesspool is a holding tank that must be emptied regularly by a special tanker. This chapter looks at the three main types of drainage: 1. below ground; 2. above ground; 3. surface water. Technical words for parts of a drainage system This section defines the parts of a drainage system in a typical small building. Drain a pipe laid below ground level that uses gravity to carry waste water away from the build¬ ing. Gully the fitting on the drain that takes waste pipes from baths and basins, but not WCs. Invert level the depth to the bottom of a drain pipe measured from the datum. Manhole the access point to the drainage system for inspection and cleaning. It is also called an inspection chamber. Public sewer the large pipe laid below the roads or other public land which carries waste from building plots to the treatment works. Soil drainage the pipework that takes the dis¬ charge from the soil and waste fittings such as the WC, bath and basin. Soil vent pipe installed at the end of the drain¬ age system for a building to expel gases from the sewage system. Surface water drainage the water that flows from the roof and paved areas after rain. This water is considered clean and does not have to be treated at the sewage plant. Trap a fitting that retains water in the drainage system. The trap prevents sewer gases entering a building or escaping at ground level. Principles of soil drainage Since drains laid below ground are fairly inaccessi¬ ble, their operation must be as trouble-free as 147 148 Building construction Figure 17.1 An overview of the discharge of waste water from a house to a public sewer. possible. To achieve this you need to follow these principles in their construction: 1. Ensure that the drains are watertight so that waste does not leak out and contaminate the ground. 2. Clear away obstructions within the pipes such as surplus mortar at the joints. 3. Lay drains on even gradients to make sure that the water carries solid matter away smoothly. 4. Lay drains in straight lines. If a drain changes direction, then insert an inspection chamber. 5. Construct a manhole if several pipes come together to join a single drain run. 6. Construct inspection points that are less than 43 metres apart. Construct manholes at 90 metre intervals on straight runs. 7. Construct a manhole at the boundary of the property before the drain joins the public sewer. 8. Use soil drains that are at least 100 mm in diameter. 9- Surround drains under buildings in at least 150 mm of concrete. 10. Backfill trenches for drains near or below foun¬ dation level with concrete. 11. Join branch drains to the main drain at an oblique angle. 12. Insert a trap at every inlet to a drain other than a soil pipe. Pipe sizes and falls A minimum 100 mm drain is usually adequate for a domestic plot. About 20 small houses can be connected to a 100 mm drain because only one or two properties will discharge water at the same time. If required, then a larger pipe such as one with a 150 mm diameter is available. The typical gradients for the waste fall are in Table 17.1. The gradient, which is a downhill slope, determines the speed of the effluent dis¬ charge. When the drains are laid to the correct fall, then the velocity of the water flow will keep the drain free of solids so that" it is self-cleaning. The fall of the drain should follow the natural slope of the ground to reduce the amount of excavation needed. 149 Drainage Table 17.1 Recommendations for gradients Pipe diameter (mm) Gradient 100 1:40 150 1:60 225 1:90 Depth of pipes in the ground Table 17.2 describes the guidelines for the mini¬ mum depth in different locations. Table 17.2 Minimum depth for rigid pipes A drain run may be steeper when short branches are connected to manholes. Generally, it is cheaper to make drain runs as short as possible with a minimum of manholes. Pipe size (mm) Fields or gardens (mm) Driveways and minor roads (mm) 100 400 700 150 600 1000 Calculating the depth of a drain It is cheaper to connect the sanitary fittings to the main sewer by the shortest possible route. Your objective is to find the invert levels for both ends of the drain run. You begin by measuring the drain run from the house to the plot boundary. The following example shows you how to complete the calculations. Example: How to calculate invert levels Find the invert level nearest the house: If you want 400 mm cover over the pipe and the outside diameter of the drain is 125 mm, then the invert will be 525 mm below ground. Where the ground level is 150 mm below the finished floor level or datum, add 150 mm. Find the invert level at the lower end of the drain run: Drain run = 30 metres Invert level below datum at head of drain = 675 mm Fall to drain in mm over 30 metres = 30 000/40 = 750 mm Invert at lower end of drain = 675 + 750 = 1425 mm below datum The depth of the drain is related to the site datum level, not ground level. (Refer to Chap¬ ter 6 for more information on site datum levels.) You must still make sure that the drain has enough ground cover. You should lay flexible pipes at least 600 mm deep in fields and gardens and 900 mm under roads and driveways. If pipes are closer to the surface than recom¬ mended, then they must be protected. You should surround rigid pipes with concrete 150 mm thick and provide expansion joints at 5 metre intervals. You should surround flexible pipes with concrete or protect them by putting them under precast concrete paving slabs that rest on 75 mm granular fill material. Types of drainpipe Drainpipes can be made from a variety of materi¬ als. Your choice of drainpipe will depend on avail¬ ability, price and suitability for the purpose. This list describes some of the most common materials for drainpipes: 1. vitrified clay, which is clay that was fired at a very high temperature to make it waterproof; 2. cast iron, which is a very hard metal alloy. This material is quite expensive and normally only used for commercial buildings; 3. concrete, which is cast using the methods of production for concrete described in earlier chapters; 4. pitch fibre, which is made from waste paper or wood fibres and bitumen or pitch; 5. plastic, which is polyvinyl chloride (PVC). This is a popular material because it comes in long lengths, is light and it makes joints easily. Methods of joining drains The method that you use to join drains depends on whether you are using: 150 Building construction 2. polypropylene sleeves, which are fitted with rubber rings to grip the pipes instead of spigot and socket joints. rigid pipes with rigid joints; rigid pipes with flexible joints; flexible pipes with flexible joints. You can use these combinations to make flexible joints for concrete pipes. Rigid pipes with rigid joints Rigid pipes made from clay, concrete or cast iron need rigid joints with socket ends that are wide enough to insert pipes with straight ends, called spigots. There should be enough space around the spigots to put the jointing material. You make a joint for a clay pipe by wrapping rope or yarn around the spigot and pushing the pipe into the socket of the adjoining pipe so that it fits tightly. Then fill the socket with a 3:1 cement mortar mix and finish it off neatly. Joints for con¬ crete pipes are made in the same way as clay pipes. Cast iron joints are formed by wrapping yarn around the spigot and filling the space between the spigot and socket with molten lead. Flexible pipes with flexible joints Flexible pipes distort under loads. This distortion should be limited to 5 per cent of the pipe’s diameter to maintain the flow of water. Similarly, the flexibility of the joint should only take up slight movement so that the pipe maintains the correct falls. You can join pitch fibre pipes with polypropylene sleeves with gaskets or by tapering the ends of the pipe and driving them into collars. PVC pipes are made with socket and spigot ends. They can be jointed by using a solvent to weld the pipes to¬ gether so that one pipe sits tightly inside the other or by inserting rubber rings in the grooves of the sockets and spigots. Rigid pipes with flexible joints Recent developments in pipe technology have made it possible to use rigid pipes with jointing methods that allow some flexibility. This is useful because rigid joints may crack with slight movement. You can choose from two types of flexible joint: Excavating the drain layout Table 17.3 shows you the basic procedure for excavating the drain layout. You can see what a typical fall for a drain run would look like in Figure 17.2. 1. spigot and socket combinations, which are fitted with plastic pieces which have grooves for rubber rings; Datum level 30 000 Figure 17.2 A typical fall for a drain run: working out the depth of the drain. Drainage Table 17.3 How to excavate the drain positions Step Action 1 Mark out the positions of the drain runs on the ground and mark the manhole positions. 2 Calculate the depth of the inverts at the highest positions. 3 Set up sight rails on the first straight drain run using a levelling instrument. The difference between the sight rails divided by 80 is the difference in level. 4 Calculate the depth of the excavation and add 100 mm for bedding if required. 5 Measure the height of the upper sight rail above the datum. Make a boning rod which stretches from the sight line to the bottom of the excavation. Example: if the sight line is 1500 mm above the datum, then the length of the boning rod will be 1500 + 775 mm (for depth of excavation) = 2275 mm. 6 Excavate the trench until you reach the correct level and line up the boning rod with the line between the sight rails (Figure 17.3). As you move the boning rod you will dig the correct level for the slope. 7 Insert some pegs in the bottom of the trench that project 100 mm off the bottom. 8 Fill the bottom of the trench with 100 mm granular material (until it covers the pegs). 9 Shorten the boning rod so that it reaches from the highest sight rail to the invert of the drain. Attach a batten to the bottom of the rod so that it can sit on the bottom of the trench. 10 Lay the drains on the bedding and keep checking the levels with the boning rod. Joint the pipes so that the socket faces the flow. 11 Test the drains and backfill. 12 Repeat procedure for the next drain run. 151 you need to check and test the support for the pipes and the gradient. After your inspection you can pack in more bedding so that it comes about half way up the pipe. The bedding that covers the top of the pipe can contain small stones less than 40 mm in diameter in 100 mm layers until there is at least 300 mm cover over the pipes in the trench. Figure 17.4 shows you the difference between bedding rigid and flexible drainpipes. Laying drains near buildings Drains for domestic buildings are usually above the level of the foundations, except for raft founda¬ tions. If they are lower than strip foundations, then you should follow this procedure: 1. Backfill the trench around the drain up to the level of the foundation if the drain excavation is closer than 1 metre to the edge of the concrete strip. 2. Fill the trench with 150 mm of concrete if the angle of the drain excavation is less than a 45° angle from a bottom corner of the foun¬ dation. Testing drains Drains that carry sewage must not leak into the surrounding ground. To make sure that the joints are secure, drains should be tested before they are covered up. The test is usually set up by the builder and checked by a building inspector. You can use three different methods to test drains: 1. the hydraulic test; 2. the ball test; 3. the mirror and torch test. tedding drainpipes The best pipe bedding is a granular material such as concrete aggregate. You should lay a 100 mm layer of bedding in the bottom of the trench to provide firm support for rigid pipes. If you trim and level the bottom of the trench carefully, then the pipes can be laid in the ground without adding infill material. You should pack and level the bed¬ ding firmly along the entire length of the pipes and scoop out holes to give extra space around the sockets. When you lay the pipes in the bedding, then To check that the drains are watertight you follow these steps for the hydraulic or water test: 1. Plug the lower end of a drain run. 2. Insert a temporary joint and 1.5 metre length of pipe at the higher end. 3. Pour water in the drain until the upright pipe is full. 4. Leave it for two hours. 5. Check the levels. 6. Top the water levels up. 7. Check the levels again after half an hour. The level should drop less than 6.4 mm per 152 Building construction Sight line Boning rod 1 1 1in _ Drain run . ... . pH m t Granular bed Figure 17.3 Checking the depth with a boning rod. (a) (b) Figure 17.4 Bedding rigid and flexible drainpipes: (a) rigid drainpipe; (b) flexible drainpipe. metre of 100 mm pipe or 4.5 mm per 150 mm pipe. If the drop in the water level is greater than this, then you must inspect the pipe for leaks and repair or replace it. The ball test checks that the pipe interior is clear of obstructions that could cause a blockage. You roll a ball that is slightly smaller than the diameter of the drain down its length. If the ball stops, then the drain is blocked and must be cleared out. The mirror and torch test checks that the drain is straight. If a mirror is fixed at one end of the drain and you shine an electric torch from the other end, then you should see the reflection of the torchlight in the mirror. Clearing out drains You can usually clear blocked drains with cleaning rods, which are flexible bamboo canes with brass 153 Drainage screw connections so that you can make longer rods if necessary. If you attach tools to the end of the rods, then you can clear, scrape and clean drains. Example If a manhole opening is 600 x 450 mm and the walls are 102.5 mm thick, then the overall size of the manhole should be 805 x 655 mm. The base size should be 905 x 755 mm. Building a manhole A manhole or inspection chamber is located on a drain run at points where several drains meet or there is a change of direction. You use a manhole to inspect and clean the underground drainage system. Figure 17.5, on page 154, shows you the con¬ struction details for a manhole. The depth of a manhole depends on its position on the drain run. The farther it is from a building, the deeper the manhole because of the fall in the drain. The size of a manhole depends on the depth of a drain and the number of connections. If the drains are very deep, then a manhole must have working space inside it. However, this is not com¬ mon in domestic drainage systems. If the drain is straight and there are no connec¬ tions, then the manhole must still be a minimum size of about 300 mm. Table 17.4 shows you the typical recommenda¬ tions for manhole dimensions. Table 17.5 describes the procedure for making a brick manhole. Table 17.5 Making a brick manhole Step Action 1 Cast the concrete base. 2 Build up the walls and build in the drains which pass through them. 3 Bed the open channel sections and branch connections of the drains in the base. 4 Fill in the spaces between the branches with concrete (this is called haunching). The haunching in between the branches and the wall should be smooth and slope to the channels to keep the bottom of the manhole clean and dry. 5 When the brickwork is completed, render it in a 1:3 cement and sand mixture to make it watertight. 6 Make a brick shelf at the top or lay a precast concrete slab over the top of the manhole if the frame for the cover is smaller than the base. Making a brick manhole You begin by excavating to the recommended depth in the correct position. The bricklayer will need enough space to work in. You should also leave space for a concrete base that is larger than the outer brickwork. In normal conditions you should add about 100 mm to the size of the manhole cover to find the correct size for the base. Septic tanks A septic tank is a brick-lined tank set into the ground, which receives the discharges from a build¬ ing. After treatment by natural processes, the dis¬ charge leaves the septic tank and filters into the soil (Figure 17.6). Table 17.4 Manhole dimensions Depth of manhole (metres) Length of manhole (mm) Width of manhole (mm) Cover size (mm) Up to 1.0 450 450 450 x 450 1.0 - 1.5 1200 750 600 x 600 154 Building construction Excavation (a) Drains --D-=t=\ Ln i * t (b) (c) Figure 17.5 Details of typical manhole construction: (a) section of a manhole excavation; (b) branch drain entering an open channel; (c) brickwork and backfill in a manhole; (d) section of a manhole showing the branch connections; (e) section of a manhole after construction. Drainage 155 Concrete cover Brick walls with spaces for liquid to pass through Rubble Concrete base (c) (d) Backfill Ballast Figure 17.6 Septic tank and soakaways: (a) septic tank; (b) seepage pit; (c) subsoil irrigation system; (d) subsoil drain and open joints. 156 Building construction If a house does not have a piped system for removing waste, then you can install a septic tank. Septic tanks can serve one plot or a small commu¬ nity, depending on the size. The smallest septic tank should have a capacity of at least 3000 litres or 3 m3. A 2 metre deep tank which is 2 x 2 x 1 m has an internal volume of 4 m3 or 4000 litres. A septic tank works by using anaerobic bacteria, which do not need oxygen, to break down solid sewage into liquid and sludge. Raw sewage enters one end and emerges as a liquid effluent at the other end. A drain takes the liquid to a soakaway where it filters into the soil as you can see in Figure 17.6. Inside the tank, gases cause the solids to liquefy and break up. After the solid settles as a sludge, then anaerobic bacteria break it down until it forms a scum on the surface, which should be pumped out at six month intervals. The residue in the tank starts the bacterial action again in a continuous cycle. The daily waste water in an average household should take about 24 hours to pass through the tank. If the water flows through too quickly, then you can put extra chambers in the tank to slow down the flow. If a person uses 200 litres of waste water per day, then a household with seven people produces about 1500 litres. This volume re¬ quires a 3000 litre septic tank. Septic tanks should only take sewage. Rainwater should go into soakaways. Grease from kitchen drains should be collected in a grease trap gully because it can clog up the septic tank and stop its effective operation. It is essential to clean gully traps regularly. Septic tank location The location of a septic tank depends on these principles: Access for pumping it out needs to be convenient. It should be at least 15 metres from a building: # It should be downwind. The effluent should not discharge into water supplies or streams. Building a septic tank First you need to calculate the size of a septic tank. You can see how to do this in the following example. Example: Calculating the depth required for a 3000 litre septic tank 1. The drain enters the tank at a depth of 600 mm. The depth of liquid will be 1.5 metres. The area of the tank should be 3 m3/1.5 m = 2 m2. 2. The length of the tank should be two or three times its width. The width is 900 mm. The length is 2200 mm. 3. The concrete base is 150 mm. Calculate the dimensions of the base in the same way as described for manholes. Note that the mini¬ mum wall thickness is 215 mm. 4. The depth of the excavation is 2250 mm (600 + 1500 + 150). You follow the steps in Table 17.6 to build the tank. Table 17.6 How to build a septic tank Step Action 1 Excavate the hole for the tank, observing the safety precautions in Chapter 7. 2 Cast a concrete base. 3 Build up 215 mm walls for the outside surface of the tank. 4 Build 102.5 mm internal walls. 5 Cover the top of the tank with 75 mm reinforced concrete panels, which are loosely set on the top of the walls for ventilation and to make it easy to remove scum. 6 Insert entry and exit pipes with T-junctions and extensions to push the sludge to the bottom. Discharging the effluent Effluent is discharged into soil soakaways such as seepage pits or subsoil irrigation systems. The efficiency of the disposal of the effluent depends on the ability of the soil to absorb it. Before you decide where to build a septic tank, you should carry out a percolation test as follows: 157 Drainage 1. Dig six holes that are about 600 to 900 mm deep in the area where the effluent will dis¬ charge. 2. Fill the holes with water. 3. Twenty four hours later, reduce the water level to 150 mm. 4. Insert a measuring stick in each hole and calcu¬ late how long it takes for the water to fall 25 mm. Using this method you can refer to Table 17.7 to determine the absorption capacity. Table 77.7 Absorption capacity Time taken for water level to fall 25 mm (in minutes) Absorption area per person (m2) 2 or less 4 3 5 4 6 5 6.5 10 8 15 9 30 13 60 17 More than 60 minutes Not suitable for effluent disposal the joints left open before you cover the pipes with 50 mm of ballast. Fill up the trench with soil to ground level. CHECK YOUR UNDERSTANDING A system of sloping drains provides drainage under the ground. Waste matter and water are carried away from a building by gravity. The drains may connect to a public sewer which carries the effluent to the sewage plant for treat¬ ment. A septic tank can take waste water if there is no public sewer. Drains must have the correct falls and comply with local building regulations to ensure safe and efficient operations. The pipes used for drains can be made from rigid or flexible materials. The pipes can have rigid or flexible joints. Manholes provide access to drains for inspection and cleaning. A septic tank treats sewage on site by using bacteria to break it down. Drains must be tested for leaks before being covered over. Seepage pits Above-ground drainage Seepage pits are most successful on steeply slop¬ ing sites or very small plots. When the effluent enters the pit, then it gradually seeps into the surrounding soil. The pits consist of one or more holes dug in the ground and lined with brick or blocks. The spaces between the material should be filled with stones. Put a concrete cover over the pit and add at least 300 mm soil on top. Subsoil irrigation A subsoil irrigation system consists of lengths of drains connected to the septic tank. About 5 metres of drainpipe is needed for each person using the tank. You can connect more than one drain run to the system. You construct a subsoil irrigation system by digging a trench 450 x 450 mm that has a slight fall. Then lay a 150 mm layer of ballast in the bottom. Put the drainpipes on the ballast with The purpose of this section is to describe how waste water goes from the sanitary fittings to the underground drainage connections. You can see an overview of this process in Figure 17.7. You install above-ground drainage after the roof is put on the building to protect the fittings from the weather. The pipework runs along the surface of the walls so that it is accessible for cleaning and clearing. Above-ground drainage is connected by one of these two methods: 1. The 100 mm outlets for WCs are connected by branch pipes to vertical pipes, called soil stacks, that connect to the drains inside or outside the building (Figure 17.8). The underground drains have sockets that fit spigots on the soil pipes. The water seal or trap formed in a WC pan ensures that gases and smells from the drain do not enter the building. 158 Building construction Table 17.8 Standard trap sizes Fitting Minimum waste trap diameter (mm) Maximum length of waste pipe (mm) Slope (mm) Basin 32 1700 20 Basin 38 3000 40 Sink 38 3000 18-90 per metre run Sink 50 4000 18-90 per metre run Bath 38 3000 18-90 per metre run Bath 50 4000 18-90 per metre run WC 100 No limit Trap should be angled 104° Drainage 2. Other sanitary fittings such as baths, basins, showers and sinks have smaller outlets, which cannot be directly connected to the drains. They are connected to the underground drains by one of these methods: A) the wastes flow through above-ground pipes and discharge over or flow into trapped gullies at the top end of the drains; B) wastes flow from above-ground pipes into the soil stack that carries the WC waste. The pipework to sanitary fittings The soil and waste pipes that carry the discharge from sanitary fittings are usually made from unplasticised PVC (uPVC). UPVC pipes come in a range of sizes to suit the plumbing requirements. Typical diameters are: 32 mm 159 38 mm 50 mm 75 mm 100 mm You can choose from four types of joint for uPVC pipes (Figure 17.9): 1. push fit with rubber ‘O’ rings for pipes with larger diameters (75-100 mm); 2. spigot and socket joints; 3. welded joints, which are spigot and socket con¬ nections that are welded firmly together with a solvent; 4. compression joints, which are used for smallerdiameter pipes like the traps on the waste pipes for baths and basins. A compression joint is a male collar which screws onto a female ring. This compresses a rubber washer to form a tight seal. Figure 17.8 Details of soil vent pipes placed (a) inside and (b) outside buildings. 160 Building construction Figure 17.9 Standard joints for uPVC pipes: (a) push fit joint with an 'O' ring; (b) spigot and socket joint; (c) welded joint; (d) compression joint. The purpose of traps All sanitary fittings have traps, which are either built in or separate. The trap is a water seal be¬ tween the drain and the sanitary fitting to keep out gases and smells, which are unpleasant and un¬ healthy. The traps for sanitary fittings are usually the standard sizes given in Table 17.8. It is important to ensure that the trap fittings connected to the internal pipework maintain a secure seal. When water is discharged from a sanitary fitting by flushing a toilet or draining a basin, then some of the water should stay in the trap to maintain the seal. However, it is difficult to prevent air gaps for gases and smells to pass through. Air gaps can be created in two different ways: 1. Self syphonage is created by a steeply sloping waste pipe so that the water runs away too swiftly, which sucks the water out of the trap. This can be remedied by a 75 mm deep trap and a more shallow slope on the waste pipe to reduce the rate of flow of the water. 2. Induced syphonage is created by negative pres¬ sure in the soil stack, which breaks the seal. This problem is solved by limiting the number of fittings connected to a stack and following the guidelines in Table 17.8. Again, a reduced rate of flow prevents the breaking of the seal. Traps and sanitary fittings Traps are usually made from uPVC. They attach to the waste fittings of sanitary appliances and match the diameter of the pipe joints. Two types of traps are in common use: 1. the bottle trap, which is shaped like a bottle. The lower part, containing the trap, unscrews for easy cleaning; 2. the ‘U’ trap, which is formed by bending a pipe into a ‘U’ shape. 161 Drainage Ventilating the indoor drainage system An indoor drainage system needs to be ventilated to prevent gases from the sewer entering the building. You ventilate the system by extending the drain that takes the waste from the WC, called a soil vent pipe, above the level of the roof. The soil vent pipe may run up an external or internal wall. The soil vent pipe allows the gases to escape safely into the atmosphere. The top of the pipe should have a wire cage to prevent birds entering and blocking it. A single-stack plumbing system A single-stack plumbing system for draining the internal sanitary fittings simplifies the pipework while ensuring that the water seals are not affected by self or induced syphonage. You need to ar¬ range the fittings so that the lengths of the waste pipes are not too long and that they are within the guidelines in Table 17.8. To make sure that the seal stays intact you should follow these recommendations when you install a single stack plumbing system: 1. Changes in direction in a pipe must be above the highest connection to the soil pipe. 2. Connections must be more than 200 mm from a branch of a WC. 3. The bend at the foot of the soil stack must have a wide angle. 4. All traps must have a seal which is 75 mm deep except WCs which are made with 50 mm seals. The sanitary fittings The main sanitary fittings in a house are the: • WC; • bath; 0 sink; 0 basin; 0 shower. They should be made of materials that are easy to clean, durable and waterproof. A WC is usually in two parts: 1. the pan and seat. The pan is made of vitreous china and includes a 50 mm trap. The outlet, which is either a ‘P’ or ‘S’ shape, is 100 mm in diameter. The seat, which can be china, plastic or wood, is hinged and bolts to holes in the top of the pan; 2. the cistern, which is made from plastic or china. It consists of the body, the lid and the internal mechanisms. The body has connections for the water supply and overflow pipe. The internal mechanism consists of a ball valve, float and a flushing siphon with an operating handle. A bath can be made of cast iron, pressed steel or plastic. The standard size is 1700 x 700 mm. The bath has holes for fixing the taps, overflow and waste outlet. A basin is made of vitreous china and has an overflow built in. A sink in a kitchen is usually stainless steel so that it will be lightweight and durable. It may come with a draining board, which stands on a timber cupboard to conceal the waste and supply pipes. A shower may have an independent plastic, concrete or glazed fireclay base. It can be attached to mixer taps on a bath or it can flow directly from pipes attached to the wall onto the floor. Access to the trap can be a problem if the tray is shallow. In suspended timber floors the trap can be housed between the joists. In concrete floors, the trap may need to be below the ceiling. CHECK YOUR UNDERSTANDING Above-ground drainage consists of the soil and waste pipes from the sanitary fittings. Above-ground drainage is connected to the underground drainage at floor or ground level. Above-ground drainage should be connected to a trapped gully. All fittings discharge water through a trap which prevents smells and gases from the drains entering the building. 0 The soil vent pipe allows any pressures from gases in the system to be released above roof level. 0 Syphonage should not occur when waste and soil pipes are connected. 0 Sanitary fittings are made of materials that are waterproof, durable and easy to clean. 0 Waste and soil pipes above ground are usually made of uPVC. 162 Building construction Rainwater disposal If rainwater flowed off the roof of a building in an uncontrolled way, then it could flood the areas around the building and inconvenience the occu¬ pants. Water can also flow off shallow eaves and find its way into a building through the walls and windows. For these reasons, it is better to collect water at the eaves in a gutter and direct it down to Figure 17.10 An overview of rainwater disposal. the ground in a rainwater pipe. The rainwater can then drain away underground and discharge into soakaways. Figure 17.10 shows you an overview of this process. Soakaways A soakaway is a rubble-filled pit in the ground which absorbs water quickly. The tests for the right Drainage 163 Figure 17.11 Details of bracket gutters and a connection: (a) a gutter bracket connection; (b) a half-round gutter; (c) a box gutter. type of ground are described earlier in this chapter in the section Discharging the effluent. You can calculate the size of the soakaway that you need by multiplying the size of the area to be drained, by the average annual rainfall in metres and dividing by 3- Example The area to be drained = 200 m2 The average rainfall per hour = 73 mm 200 x 0.075/3 = 5 m3 The soakaway should be at least 3 metres from the building. The soakaway capacity is measured below the level of the inlet pipe. at 900 mm intervals. A gutter will have an outlet which is a spout that points down to connect with a rainwater pipe. In most domestic buildings, one outlet is usually enough to take the rainwater during normal wet weather. The distribution of water along the length of the gutter pushes it naturally towards the outlet. Any residue of water soon evaporates. Some gutters are not attached to the edge of roofs such as: % gutters formed in the surface of flat roofs beside parapets; • valley gutters, which are formed at the junction of two roof slopes. The most common gutter shapes are the halfround and the box (Figure 17.11). Rainwater pipes Gutters A gutter is a channel fixed to the long edge of a roof. The bracket fixings on the fascia should be The rainwater pipes are attached to the gutter outlets and fixed vertically on the building. The roof overhang requires a rainwater pipe to bend in 164 Building constmction more than one direction to reach past the gutter to the surface of the building. This bend is called a swan neck junction (Figure 17.12). You fix the pipes with brackets, plugged and screwed to the wall surface, which hold them off the surface to allow for painting and cleaning. The water runs out of the bottom of the pipe from a shoe or angled pipe into a gully fitted with a grating. If this gully is connected to a soakaway by an underground pipe, then it does not need a trap. If it is connected to the soil drainage, then it must have a trap. The flow should run down against the face of the rainwater sockets. The joints do not need to be sealed except to stiffen the pipes. If there is a blockage in a pipe, then the water can leak out through the joints and alert you to the problem. If the pipes are inside a building, then the joints must be watertight. Materials Gutters and rainwater pipes are most commonly made from: ® uPVC; fibre cement; zinc. UPVC is the most popular material because it does not need decoration, it is lightweight and easy to fix. UPVC does not rot or corrode. However, this material is more easily damaged and is unsuitable for areas where it could be hit by moving vehicles. UPVC also expands and contracts more than the other materials as a result of temperature changes. Fibre cement is a durable and heavier material than plastic that requires more joints and supports. It is often used for larger roofs that take big gutters, like those on industrial buildings. Fibre cement is not affected by temperature changes and it can be painted or left in its natural grey colour. You need to be very careful if you cut it that you do not inhale toxic dust. Zinc is not a strong material because it dents easily and corrodes in some climates. It is popular since it can be made almost anywhere by folding and soldering zinc sheets into the desired shapes. Gutter and rainwater pipe dimensions The number and positions of the outlets from the gutter depend on the intensity of the rainfall and the size of the roof. Table 17.9 indicates suitable dimensions for gutter outlets and rainwater pipe sizes in average conditions. Table 17.9 Gutter and rainwater pipe (outlet) dimensions Figure 17.12 A swan neck junction. Gutter width (mm) 100 115 125 150 Diameter of outlet (mm) 50 63 75 89 Area of roof to be drained (m2) 20 40 60 90 The length of a gutter from the eaves to an outlet should be less than 6 metres. If necessary, a gutter can have outlets at each end or at intervals over long distances. 165 Drainage Internal gutters and downpipes on enclosed flat roofs are more likely to block up and cause water damage. It is safer to increase the size of the pipe for internal gutters and downpipes. Gutters for flat roofs If a flat roof does not have a parapet, then a gutter can be fixed to a fascia with brackets. If there is a parapet, then a gutter is formed as part of the roof construction. This is called a parapet gutter (which you can see in Figure 17.13). It is usually wider and shallower than the gutter fixed to the outside of a building and is lined with the material forming the roof covering, such as felt or asphalt. These gutters must be at least 300 mm across. The fall to the outlet should be about 1:80 to match the slope of the roof. The outlet can: 1. be inside the parapet wall; 2. pass through the parapet to an external rain¬ water container. If the outlet is inside the parapet wall, then a deeper recess at the end of the gutter called a cesspool collects the water and makes a smooth flow into the rainwater pipe. A wire ‘balloon’ in a hole in the bottom of the cesspool will collect leaves and other material. The balloon should be cleared from time to time. The rainwater pipe passes down inside the building, bends out through the foundation wall and runs underground to the soakaway. If the outlet passes through the parapet, then you make an opening in the parapet wall at the lower end of the gutter. It can be directly in line with the gutter or at right angles. You should dress the roof covering material around the opening and insert flashings around the sides to fit the upright part of the roof covering. You fit a container or rainwater hopper to the outside of the wall just below the outlet. The bottom of the hopper has an outlet that is attached to the rainwater pipe. Gutter Rainwater head Cesspool Figure 17.13 A parapet gutter on a flat roof. Rainwater pipe 166 Building construction Valley gutters When pitched roofs meet at right angles, then the junction is called the valley, as you can see in Figure 17.14. You make a gutter in the valley that runs from top to bottom. Since this is almost an internal gutter, water could enter the building if it overflowed. These gutters must be a minimum 300 mm across to avoid blockages and overflows. Surface water Water that falls on the hard surfaces surrounding a building such as paths, terraces and driveways can be collected by open channels or gullies. Hard surfaces should slope away from the walls towards these collecting points. If the drains running from the gullies go to a soakaway, then they do not have traps, but they should be fitted with remov¬ able silt buckets to make them easier to clean. • Pitched roofs should have gutters and downpipes. • Water on flat roofs without parapets should fall to eaves’ gutters. • Flat roofs with parapets should have a built-in gutter with a cesspool if the rainwater pipe is external. • Rainwater pipes should not be connected to the soil drainage system. • Rainwater pipes should take the water to soakaways at least 6 metres from the house. • Gutters and rainwater pipes are usually made out of uPVC, zinc or fibre cement. If pitched roofs form an internal angle, then a valley gutter is formed. The size of gutters and downpipes should match the roof area to be drained. Hard surfaces should slope to drain off water into gullies and channels. REVISION EXERCISES AND QUESTIONS CHECK YOUR UNDERSTANDING Rainwater that falls on and around a building should be collected and piped away. Figure 17.14 A valley gutter on a pitched roof. 1 2 Why are drains laid so that they are not too steep or too shallow? The invert of a 45 metre long 100 mm drain is 875 mm below the datum at the higher end. Drainage 3 4 5 6 7 What is the depth of the invert at the lower end? What materials are used for flexible and rigid drain pipes? What are three methods for testing drains? What are three parts of a manhole? How does a septic tank work? How do you use boning rods to excavate a drain run? 8 9 167 Explain the following: i) the purpose of manholes on a drain run ii) the reason for venting a drainage system iii) how branch drains connect to the main drain? How does the waste from a WC and a sink join the drainage system? Introduction Water is essential to a household. You use it for drinking, cooking and washing. This chapter looks at how clean, cold water is supplied to domestic buildings from the main water pipes. Figure 18.1 gives you an overview of this process in a community. The installation of safe and efficient hot water systems is also important. As well as looking at hot water systems that depend on electricity in this chapter, you can also find out more about the use of solar power as a source of energy. The cold water supply Cold water is supplied under pressure, which car¬ ries it up to a storage tank in the roof and pushes it out of any taps connected to the mains supply. This pressure can be gravity-fed from storage res¬ ervoirs or pumped from pumping stations. A water company will limit the pressure to protect pipes and fittings, but normal working pressure should allow water to reach the top of a twenty-storey building. The amount of water pressure that you need for a two-storey house is 10 per cent of the pressure available. Main water pipes usually run under roads or footpaths so that the supplies can be drawn off to individual plots. When a new supply is needed, a water company will run a service pipe from the mains to a point just inside the plot boundary. They put in a stopcock and possibly a water meter to measure the amount consumed. The contractor lays a 12 mm pipe from the stopcock in a trench, which is at least 600 mm 168 below ground level. The pipe passes through the foundations and rises inside the building in a duct. The rising main The pipe for the water supply inside the building is called the rising main as you can see in Figure 18.2. It goes up through the building and connects to the storage tank in the roof space. A branch goes directly from the rising main to the cold tap at the kitchen sink to provide drinking water. The storage tank (Figure 18.3) You should place the storage tank as high as possible in a building to provide enough water pressure to all the fittings. The tank can go in the roof space under a pitched roof or on top of a flat roof. Because a full tank of water weighs more than 500 kg, the roof or ceiling must be strong enough to take this load. Domestic tanks, which have a 450 litre capacity, are made from galvanised steel, fibreglass or poly¬ thene. The tank supplies all the cold water except to the kitchen sink. The supply from the tank is called the down service. The main supply enters the storage tank near the top. The flow is controlled by a ball valve fitted with a float. The float rises up with the rising level of the water as the tank fills until a lever attached to the float closes the valve and cuts off the supply. When water is discharged, then the float lowers with the falling water level and the valve opens to let water into the tank. The tank has an overflowjpipe, which discharges water outside if the ball valve fails. This avoids flooding inside the house. The tank has a cover to prevent birds and small animals falling in and contaminating the water. _C _c o o 5 H— CD w -t—' CD o § q3 (/) > CD Q. CD Figure 18.1 An overview of water collection and distribution in a community. Water supply 169 170 Building construction The supply pipes exit the tank just above the bottom. This ensures that dirt or grit settles to the bottom, but is not drawn off into the pipes and fittings. Controlling the water flow Stopcocks on various points of the supply pipes allow you to turn off the water for repair or Figure 18.2 An overview of the supply and disposal of water. 171 Water supply Cover Overflow hot water tank replacement of the pipes. You should fit a drain outlet at the lowest point of the pipework to drain off the water in the storage tank and pipework. Before you drain off a water supply you must tie the ball valve in the tank in the closed position and shut off the rising main at a stopcock, which is a short pipe that can be opened or turned off with a handle or key. Stopcock locations You can fit a stopcock on the rising main where it enters a building. This lets you shut down the supply to the kitchen sink and storage tank. You can also fit a stopcock near the storage tank. This lets you work on fittings connected to the down service without draining down the storage tank. Ball valves control the water flow in indi¬ vidual fittings such as: the storage tank; @ the WC cistern. Hot water installations Hot water can be produced in various ways, but in modern buildings it should be a safe and efficient part of the normal plumbing installations. This section examines the methods for supplying hot water to sinks, baths, basins and showers in do¬ mestic environments. Three types of electric appliances heat water: sanitary fittings 1. immersion heaters; 2. electric boilers; 3. electric geysers. An immersion heater is an electric element in a storage cylinder, which heats the water to a pre¬ set temperature. When the hot water is used, then the immersion heater heats up the new supply of cold water to the pre-set temperature. The immer¬ sion heater has a thermostat, which senses the temperature of the water and switches the electric¬ ity supply on and off as required. The hot water is supplied from the top of the cylinder and cold water enters the bottom. This ensures that the hottest water is available for use. Cylinders fitted with insulation jackets retain heat longer and save energy. An electric boiler is a separate appliance for heating water in a storage tank. A primary pipe circuit links the boiler with the storage cylinder. The boiler heats the water in the primary circuit, which gets hotter and hotter. While it passes through a coil in the storage cylinder, the heat transfers to the cold water in the cylinder. When the water in the cylinder reaches a pre-set temperature, then a thermostat switches off the electricity supply to the boiler. As hot water is used and the temperature of the remaining water drops, then the thermostat switches on the electricity again and the boiler heats up more water. An electric geyser makes hot water by convert- 172 Building construction ing cold water to hot as it is needed. When a tap is turned on, water flows through a coiled pipe, which is covered by a heating element. Turning the tap switches on the current to the heating element, which heats the water as it flows past. The flow of water is fairly slow so this type of fitting is best suited to a single location such as a basin or sink. Gas, oil and solid fuel boilers Solid fuel boilers work in a similar way to electric boilers. Solid fuel boilers also have an alternative system that heats the water without using a pri¬ mary coil in the storage tank. The fuel used in these boilers is coal or wood, which must be fed into the boiler. The disadvantages of the solid fuel boiler are that the ash must be regularly removed and that there is no simple way to control the water temperature. A solid fuel boiler also needs an external flue. Gas and oil boilers have better control of fuel Figure 18.4 Using solar panels to heat water. consumption than the solid fuel boiler. They work in the same way as the solid fuel boiler, using a primary circuit inside a cylinder to heat water. Solar power Solar power heats water by concentrating the sun’s heat energy in a collector with coils that contain water (Figure 18.4). The most simple system uses a passive method to heat water. This involves con¬ necting a cylinder to a collector with water in its coils. As the sun heats the water, it rises up into the cylinder for storage. When the water cools, it re¬ turns to the collector. This cycle, called thermo¬ syphon, is continuous, but it means that the supply of hot water is erratic. The maximum water temperature depends on: the initial water temperature; the amount of exposure to the sun; the time of year; the amount of cloud cover; 173 Water supply Solar collector Primary circuit Upper hot water cylinder Secondary circuit Figure 18.5 Two solar water heating systems: (a) passive solar power system; (b) active solar power system. 174 Building construction the amount of daylight; the time of day. Solar power is more effective if the electric immersion is the basic water heating appliance. In the passive method in Figure 18.5, the solar col¬ lector is placed as low as possible to encourage a thermo-syphon to develop between it and the first storage cylinder. Water is drawn from a second cylinder with an electric immersion, which is be¬ low the first cylinder. The water in the first cylin¬ der, which was heated by solar power, flows into the second cylinder. Because the immersion heater does not need to use as much electricity to raise the water temperature, energy is saved. In the active method in Figure 18.5, you place the solar collector on the roof in a position that is exposed to the sun. Since the thermo-syphon prin¬ ciple will not work if the collector is above the storage cylinder you need to install an electric pump in the circuit. The pump, which works on a time clock to regulate water supply during the day, assists the operation of the electric immersion heater on the same principle as the passive system. The differences are the costs of the pump and the electricity to run it. You can also use a solar hot water system to preheat a water supply to a boiler or geyser. If the water temperature from the main sup¬ ply is 15°C and the solar collector heats it to 60°C, then the immersion heater only needs to raise the temperature 5°C to reach a com¬ fortable 65°C. This saves energy and money. The pipework for hot water systems Cold water enters the hot water cylinder at the bottom of the tank (Figure 18.6). The source may be: 1. a direct down service from the cold water stor¬ age tank; 2. a supply from a cylinder on a solar heating circuit. The various fittings that use hot water draw it off from the top of the cylinder in a series of branch pipes. When you turn on a tap the water comes out under pressure which is created by a head of water between the tap and the level of water in the cold water tank. Figure 18.6 Parts of a hot water tank. The pipe at the top of the cylinder also acts as an expansion pipe so that any water that is pushed out of the system as the temperature rises falls back into the cold storage tank. This is a safety valve for the system. If the thermostat fails on the immersion heater, and the water boils, then steam will escape from the expansion pipe into the cold tank. Pipes and fittings Half-hard tempered copper tubing is the most popu¬ lar material for the pipework. It is lightweight, solders well and can be bent by hand using a bending spring. This is essential to avoid crimping the walls of the pipe, which reduces the diameter of the pipe. The standard sizes are: 15 mm (0.5 in) 22 mm (0.75 in) 28 mm (1 in) In metric systems the pipe is measured by its outside diameter. Water supply 175 Figure 18.7 Two types of joint for copper pipes: (a) compression joints; (b) capillary joints. You can use two different joints to connect copper pipes to fittings: 1. compression joints; 2. capillary joints. The compression joints in Figure 18.7 are the easiest connections to make. One end of a fitting is threaded at the bend or tee. The end of the pipe that fits into the bend or tee has a nut and ferrule. You push the nut of the pipe into the threaded end of the fitting. This pushes the ferrule into its mouth. When you tighten the nut then the ferrule is com¬ pressed. This makes a watertight joint. This method is also good for tap, valve and cylinder connec¬ tions. The capillary joints in Figure 18.7 are less popular because you need to use a blowlamp to soften the solder that joins the pipes. Capillary joints also need a compression joint at the connec¬ tion to a tap or fitting. You make a capillary joint by pushing one end of a pipe into the end of a bend or tee with a ring of solder in a groove. You then move a blowlamp over the pipe to soften the solder. When solder appears at the edge of the joint you should allow the completed joint to cool. You can remake the joint by reheating. Iron pipes require a different method to join them. You need to cut a thread in the end of the iron pipe after it has been cut to the correct length. 176 Building construction Bends and tees are usually already grooved to receive threaded pipes. You cover the threaded end with a jointing compound and bind it with hemp or tape wound in the direction of the thread. To complete it, you tighten the fitting on the threaded pipe. CHECK YOUR UNDERSTANDING • Water for domestic buildings is mainly used for drinking, cooking and washing. • The pressure in the main supply comes from gravity or pumping. • Water for drinking and cooking may come di¬ rectly from the main supply. • Water used for other purposes can be stored in a tank. • Overflow pipes are fitted to storage tanks to avoid damage to the interior of the building. 9 You use hot water mainly for washing and cleaning. 9 Water can be heated by: i) electric boilers oj immersion heaters; ii) solid fuel boilers; iii) gas or oil boilers; iv) solar power collectors. • A hot water installation must have a vent or expansion pipe to relieve pressure in the pipework if the system overheats. • The cold water storage tank must be higher than the hot water cylinder to provide the pressure to push the water out of the taps. 9 Boilers use primary circuits to heat water. • Immersion heaters use an element in the tank to heat the water. • A passive solar system uses thermal syphonage to heat water. 9 An active solar system needs a pump to circulate water from the collector to the storage cylinder. REVISION EXERCISES AND QUESTIONS 1 What are three sources of water? 2 What does a water treatment plant do? 3 What are the purposes of: i) stored water ii) mains water? 4 What do the following parts of a plumbing system do: i) a stop cock ii) a ball valve? 5 What are the main differences between active solar water heating systems and passive solar water heating systems? 6 What are two methods for joining copper water pipes? Introduction Electricity is now seen as a basic necessity of life. It is usually generated at power stations by a national company and distributed to individual users on a national grid. The grid consists of the overhead cables on steel pylons that run across the countryside. When the grid reaches a community, the distribution is carried on underground and overground cables to individual plots. The electricity supply company usually brings the service cable from the local distribution net¬ work into a building where it installs the main switch fuse and the meters. The rest of the instal¬ lation is the responsibility of the contractor and qualified electricians. When this work is completed, then the responsibility for maintaining the installa¬ tion transfers to the owner of the building. The electricity company checks that the circuits are properly installed and earthed before the build¬ ing is officially connected to the main supply. This chapter discusses the main principles of electrical installations in a new building as well as simple electrical theory. Consumer units The supply in a house passes from the meter to a distribution panel called a consumer unit, which you can see in Figure 19.1. The supply branches inside the unit to feed several small cables which form the circuits for lights and electrical equipment. Each wiring circuit in the consumer unit is pro¬ tected by a fuse which has a fixed value: 5 amp 10 amp 20 amp 30 amp The fuse value should be matched to the antici¬ pated current in the circuit. Examples: Cookers are 30 amps. 0 Water heaters are 15 amps. Power sockets on a ring main are 20 amps. 0 Lighting circuits are 5 amps. Simple electrical theory The purpose of earthing is to ensure that excessive loads in the system are carried away. This increases the flow of current so that a fuse burns out as a safety mechanism. A copper rod buried in the ground is con¬ nected to the earth wiring which is connected to all the fittings. If a live wire touches a fitting, then the current goes down to the earth wire. A fuse in the live wire burns out which disconnects the supply. This section gives you an outline of simple electri¬ cal theory to help you understand how electricity works in a domestic environment. You can compare the flow of electricity in a wire to a flow of water that is pushed around a pipe by a pump. The pressure produced by the pump pushes the water molecules around the loop and back into the pump. When you apply voltage to an electric wire it has the same effect as the pump pushing the water. The resistance in the pipework is reduced by increasing the diameter, which allows more water 177 178 Building construction Figure 19.1 The main electrical controls in a house: (a) consumer unit for a switch meter; (b) consumer unit for a hot water heater; (c) cooker control unit. 179 Electrical installations to flow through. The same principle applies to electricity. A thicker wire offers less resistance and allows more current to flow through. I-—The relationship between the current flow and resistance is represented by this formula: 1= V/R I is the current measured in amperes (amps) V is the pressure or voltage (volts) R is the resistance, which is measured in ohms The efficiency of an electricity supply also de¬ pends on the rate that the work is done (the amount of power used). If you push water through a pipe at a faster rate, then you will need more pressure. You do this by increasing the rate of the pump, although this is limited by the size of the pipe. In electrical supplies the size of the wire limits the amount of power you can use. This is shown in the formula W= cally 33 000 or 11 000, are used to transmit electric¬ ity over long distances. In neighbourhoods, trans¬ formers reduce the voltage to a level adequate for domestic installations. The voltage in a domestic system is usually fixed at 240 volts, which is a safe rating for all appliances. An appliance designed to operate at a specific wattage will consume a specific amount of current. The wiring carrying this current must be the right size or it will overload and burn out. An electric water heater is rated at 3 kilowatts (3000 watts) The current required will be 3000/240 = 12.5 amps A radio is rated at 600 watts The current required to operate it will be 600/240 = 2.5 amps The wiring for the water heater must be five times larger than for the radio. The radio will work with the larger wire, but the water heater would burn out if a smaller wire is used. Ex / W is the power or wattage. Since mains electricity is supplied at 240 volts, then you can vary only the current or wattage. r------—- Example using a 5 amp cable: I^= 240 x 5 = 1200 watts If this cable supplies a lighting circuit with 100 watt bulbs connected to it, then the maxi¬ mum number of bulbs that can be used at one time is 12 (1200 watts/100 = 12). Direct and alternating current A direct electrical current flows in one direction only. This is the type of current produced by batteries in torches or radios. Mains voltages have alternating currents because they are easier to pro¬ duce and to use than direct current. Alternating currents move between positive and negative poles at 50/60 cycles per second. Electrical wiring The components of electrical energy The electrical system must have these components in the correct relationship to provide electricity to the consumer: 1. voltage, which is the electrical pressure; 2. amperage, which is a unit of electrical cur¬ rent; 3. wattage, which is a unit of electrical power; 4. ohm, which is the unit of electrical resistance. The amperage needs to be small to reduce the size of the distribution cables. High voltages, typi¬ Domestic electrical circuits are wired with cables that consist of three wires, which have the standard colours shown in Table 19.1. Table 19.1 Wire identification Wire colour Wire code Symbol Red or brown L for live + Black or blue N for neutral - Green or yellow/green E for earth None 180 Building construction The live wire is always connected to the live side of any switch, socket or appliance because this wire supplies the voltage and oscillation rate. The neutral wire is at zero voltage and is passive. Wiring installations and equipment should be protected by fuses, which are small cartridges con¬ taining 2, 5 or 13 amp wires in their circuits. Equipment and appliances need fuses which corre¬ spond to their wattage. Examples: Water heaters need 13 amp fuses. Radios need 5 amp fuses. Wiring domestic appliances This section describes typical wiring installations for domestic electric appliances and circuits. An electric cooker usually has a 30 amp fuse. A single cable goes from the consumer unit, which distributes electricity to the domestic circuits, to a cooker control unit near the cooker. This cable consists of three PVC insulated wires, which should match the wires described in Table 19-1, inside a PVC sheath. A loose cable connects the cooker control unit to the back of the cooker. A 3 kW water heater will have a 13 amp fuse in the consumer unit. A cable runs from the con¬ Figure 19.2 A ring main system with socket outlets. sumer unit to an isolating switch near the water heater. This switch usually has a pilot light to show if it is on or off. The supply passes from the switch to terminals on the immersion heater. A ring main, which should have at least six outlets, connects the wiring for wall sockets around a house (Figure 19.2). The wiring for a ring main is protected by a 20 amp fuse at the consumer unit. It runs around the ring, looping in and out of sockets, and back into the unit. This completes a circuit. Some items of household equipment that might use the wall sockets are: 2 amp light fittings; 5 amp stereo equipment; 13 amp refrigerator; 5 amp television; 13 amp 1000 watt heater; 13 amp electric kettle. A house may have more than one ring main in it, depending on the number of appliances and lights in use at one time. The ring main has three wires in the standard coloured PVC sheaths, which are connected to terminals in the socket outlets. You use a three-pin plug to connect a piece of electrical equipment to the supply through the socket. The plug on the Electrical installations 181 Figure 19.3 A typical lighting circuit for a house. appliance or light contains a fuse, which should match the required current. A lighting circuit has 5 amp fuses, as you can see in Figure 19.3. It should carry 3 amps and supply up to twelve 100 watt bulbs. The wiring should run from the consumer unit through the floor or roof space to small distribution boxes in the ceiling light point positions. Cables, which run from the distribution boxes to the light switches and bulb holders, carry the supply to at least twelve distribution boxes in a circuit. The main fuse in the consumer unit protects the mains from overload. The total demand for current if all circuits were on would be more than 100 amps. Although this is unlikely, the supply company installs a 100 amp main fuse as a precaution. CHECK YOUR UNDERSTANDING Electrical power is distributed by overhead power lines and transformed down to levels suitable for domestic use. The electrical supply enters the house at a con¬ sumer unit where the meters and main fuses are located. The consumer unit distributes electricity to the domestic circuits. Q Equipment is rated according to its amperage or amount of current consumed. $ Electrical supplies are rated according the rela¬ tionship between watts, volts and amps. # Earthing protects people when they use electri¬ cal equipment. 182 © Wiring has standard colour codes: i) red or brown; ii) black or blue; iii) green or yellow/green. Building construction REVISION EXERCISES AND QUESTIONS 1 2 3 4 What are the standard colour codes for electric wires? What does earthing do? If an electric heater is rated at 2 kilowatts, then calculate how much current it uses. Draw two sockets on a 13 amp ring main. Introduction This chapter looks at the treatments that you put on internal floors and internal and external walls. The treatments, called finishes, include: 6 plaster; # render; Q paint. Gypsum is calcium sulphate, which is a natu¬ ral rock. It is ground and the water is re¬ moved to make a powder. When you add water during plastering, it sets and hardens into a crystalline solid. To prevent the gyp¬ sum plaster setting too rapidly, chemicals are added to slow down the setting speed. Gyp¬ sum is also called plaster of Paris, which is used for casts for broken limbs. Finishes serve decorative and practical func¬ tions. They improve the appearance of the struc¬ tures underneath, but also prolong building lifespans. Preparing surfaces for plastering In domestic buildings you might plaster: Plastering The term plastering means the application of a smooth coat of material to walls and ceilings. The purpose of plastering is to provide a jointless, hygienic, easily decorated smooth finish to walls. Plaster covers up the unevenness of bricks, blocks or concrete. Plaster is mixed with water to make a plastic mixture, which can be spread directly on a surface in a thin 10 mm layer. The surface absorbs the water in the mix by a process called suction. The suction process stiffens the plaster rapidly so that you can level it while it hardens and sets. When the plaster dries it leaves a hard, smooth finish for decoration. Plastering materials Plaster is powdered cement, sand and lime or gypsum, which is supplied in bags. • brickwork; • blockwork; • concrete; • plasterboards. Each of these surfaces needs some preparation before you put on the plaster finish. Most bricks provide a good surface for plaster¬ ing because they have enough of a natural key (a key is a rough surface that plaster will stick to). Before plastering brickwork you need to remove any projections and clean the surface with a stiff brush. When you put wet plaster on the wall, the water from the mix is absorbed by the brickwork. You need to check that this does not cause the plaster to dry too rapidly so that it becomes un¬ workable. The process of plastering blockwork is very similar to plastering brickwork. The type of concrete that you might plaster would be the soffit of a floor slab. The concrete may be quite smooth from the formwork unless a chemical was applied before the concrete was poured. To prepare concrete, you need to wash off 183 184 Building construction all traces of oil and hack the surface to provide enough key for the plaster. Plasterboards are designed to form a base for plastering the ceilings under timber floors and roofs. Plasterboard is a solid core of gypsum plas¬ ter with a heavy paper surface on both sides. The boards are usually 12 mm thick for fixing to timber supports at 400 mm centres. Plasterboards should be fixed to the supports with small, flat head nails which are driven in slightly below the surface and filled over. Plasterboards can also serve as dry lining for walls if battens are fixed at these centres. Before the plaster is applied, you should rein¬ force the joints in the boards with a 90 mm jute fabric bedded in plaster. You then put on a single 5 mm thick coat (a skim coat) and trowel it to a smooth finish. Applying a plaster finish You may apply one, two or three coats of plaster to achieve a smooth finish. Generally, you need to apply two coats unless you are using plasterboards, which need only one. Three coats are only used if the surface is extremely uneven. The first coat in a three-coat finish, called a screed coat, is applied to level the surface and to ensure that the plaster is the correct thickness. The first coat in a three-coat finish levels out the irregularities and the absorption capacity of the backing surface. You can use: i) a mixture of sand and plaster, called brown¬ ing; ii) a plaster mixed with special aggregates like perlite or vermiculite. These mixes are usually sold ready-made. You begin by preparing the background. Any de¬ pressions in the surface should be filled with mor¬ tar or neat plaster. You then apply a cement and sand mixture (1:3 combined with minimal water) with a trowel. The sand should be well-graded to reduce cracking from shrinkage after the plaster dries. Before the first coat fully sets, you should scratch it to provide a key for the second coat. Mixes for the finishing coat You can choose from various mixes for the finish¬ ing coat. Ranked in order from the most pliable to the hardest, they are: • lime putty. Hydrated lime mixed with water stiffens very slowly. This mixture can be left overnight if you want to continue working the next day. You can add sand to reduce shrink¬ age; lime putty and gypsum plaster in a 1:1 mix. This mix is stronger and is suitable for backgrounds that do not contain lime. As long as the surface is not worked too much with a trowel, then there is little shrinkage; gypsum plaster with 25 per cent lime putty. This mix is harder and sets faster, but works well; cement, lime and sand mixes. This mix in a 1:5:3 mixture makes the hardest finish. If you increase the amount of lime and reduce the amount of sand, then the hardness is reduced. This also reduces the amount of small cracks in the finish. Tools for the job Plastering requires these tools: a bucket to carry the plaster mixture; a mixing board and shovel; a hawk, which is a small board to hold the plaster while you put it on a wall or ceiling; a wood float to apply plaster and smooth render coats; a steel float to smooth the final coat; a screed board, which is a straight piece of timber to level the plaster between screeds; a builder’s level; trestles and scaffolds to make a platform for working at the top of walls and on the ceiling. How to plaster Table 20.1 describes how to plaster a wall step by step. Finishes Table 20.7 How to plaster a wall Step 185 Plastering ceilings Action 1 Put mounds of cement and sand mortar across the wall in columns of three about 1200 mm apart (Figure 20.1). Check that the mounds are in a straight line. Smooth the mounds to a thickness of about 10 mm. Leave them to set hard. 2 Apply 75 mm vertical strips of plaster (called screeds) over the mounds (Figure 20.2) and leave them to set. 3 Mix the plaster by hand or with a small mixer. 4 Apply a rough plaster coat to the wall between the screeds by putting it on with an upward sweeping movement. 5 Move the screed board from the bottom to the top of the wall in a sawing motion to smooth and level the plaster. 6 Scratch the first coat before it sets to provide a key for the second coat and leave to dry. 7 Apply a finishing coat of 2 mm neat plaster with a steel float to produce a thick, smooth finish. The soffit of the reinforced concrete slab that forms the ceiling should be level if the formwork was well built. If the surface is very uneven, then you will need to apply three coats of plaster. The first coat will be a render coat, which creates a level surface with screeds. It should be about 10 mm thick. The second coat called the float coat, should be 6 mm thick, and the ceiling should be finished off with a final 2 mm coat of neat plaster. Fixing plasterboards to ceilings Plasterboards can make good ceilings under sus¬ pended timber floors or a pitched timber roof. The boards are fixed so that their lengths are at right angles to the floor joist or ceiling joists at 400 mm centres. You can see how this looks in Figure 20.3. The boards are quite large and heavy. They are usually 2400 x 1200 mm and weigh 25 kg. You need to put up props to hold them in position, s that two people can support them while a third person nails them into place. The boards are nailed at 150 mm centres along the lines of the joists. The Figure 20.1 Applying mortar to make a screed for plastering. 186 Building construction Vertical screed Figure 20.2 Fixing the vertical screeds for plastering. Plasterboard Joists Figure 20.3 Fixing plasterboards to a ceiling. 187 Finishes joints at the ends of the boards should be under a joist, which may require cutting to fit. You finish by binding and filling the joints before applying a skim coat of plaster. External render External rendering is the process of applying a cement and sand plaster coat to the outside walls of a building. You apply external render to: 1. improve the appearance of concrete block walls; 2. provide a waterproof finish to porous blocks such as landcrete and sandcrete blocks; 3. provide a base for a colour finish. Although gypsum is not suitable for external use, you can add lime to a cement and sand mix to improve its pliability. Several different finishes and textures are com¬ mon to external rendering. They improve the ap¬ pearance of the cement and sand mix and help to control shrinking and cracking, which affects the waterproof quality of render. Smooth render is cement and lime mixed with sand in a 1:2:9 mixture. It is put on as a finishing coat and trowelled to a smooth finish. If an under¬ coat is needed, then the proportions should be reduced to 1:1:5. This is the least satisfactory finish because the trowelling can bring too much cement to the surface, which causes cracks. Roughcast render is a top coat of cement, lime and sand in a 1:2:9 mix over a 1:3 cement and sand backing coat. While the top coat is soft, you throw 6-13 mm cement-coated aggregate into it. Scraped render is a 1:1:6 or 1:2:9 mix of cement, lime and sand. You scrape the top 2 mm off with a saw blade just before it hardens to remove the smooth skin. Pebbledash render is a final coat in a 1:1:6 ce¬ ment, lime and sand render with 6-12 mm pebbles lightly pressed into it so that the aggregate is exposed. Tyrolean render is produced by a machine that throws a 1:3 cement and sand mixture onto the wall for a deeply textured finish. The cement can be coloured to produce a permanent coloured finish. The background can be rendered or the Tyrolean render can be applied directly to a raw wall and built up in layers. Defects in rendered surfaces The main defects in rendered surfaces are: cracking; crazing; loss of adhesion. Cracks appear in render because: 1. The mix is too rich in cement which causes shrinkage cracks when the render dries. 2. The mix dries out too rapidly. This is difficult to avoid in hot sun, so the application of render should be done on a dull day or late in the day. 3. The background wall moves or settles. This can cause cracks or loss of adhesion. 4. The finishing coat is stronger than the back¬ ground or render coat. Crazing is fine cracking in the top surface of the render. This is caused by: 1. too much trowelling, which brings neat cement to the surface; 2. too much suction in the backing coat, which draws water out of the top coat. You should put water on the backing coat before applying the top coat; 3. the render drying too quickly in the sunlight. Loss of adhesion is obvious if you hear a hollow sound when you tap the surface of the render. Adhesion is lost when: 1. the key is inadequate; 2. the surface is dirty or oily; 3. the background is too porous or is not wetted before rendering; 4. water penetrates the render through cracks. Loss of adhesion is a difficult problem to fix. Painting Painting is the application of a pigmented liquid that stretches thinly across a surface when the liquid dries out. Walls, ceilings, woodwork and metalwork are painted to: 1. provide a decorative appearance; 2. protect the surface from moisture penetration; 3. protect the surface from rusting. 188 Building construction Paint materials Standard paints consist of: Primers are applied to seal unpainted metal and wood surfaces. Typical wood primers are: thinners; G pigments; # binders. 1. pink primer, which is linseed oil-based white lead with 10 per cent red lead. This is a toxic substance; 2. aluminium wood primer, which is a metal-based resin. This primer is good for sealing wood surfaces that contain resins; 3. acrylic primers, which are water-based emul¬ sions with good penetration. They are quick drying and non-toxic. The thinner is the liquid part of paint, which enables it to flow freely from the brush onto a surface. The thinner evaporates when paint dries ■which may take a few hours or days. The evapo¬ ration of the thinner causes the characteristic smell of paint, which gradually disappears. Paint must be thoroughly stirred to mix the thinner and the solid pigment. The pigment is the solid colour of the paint. The pigment, which stretches thinly to cover the surface being painted, can be any colour or black or white. Pigment comes from organic, inorganic and synthetic sources. The binder combines the pigment and other additives in the paint and determines how well the paint adheres and penetrates. Types of paint The main types of paint are: G gloss; © undercoats for gloss; 0 primers: € water-thinned. Gloss paints are based on resins produced in laboratories which have improved the quality of gloss paint. There are two main types of gloss paint: 1. paints thinned with white spirit: 2. paints thinned with water. White spirit is a substitute for turpentine which is used to dilute gloss paint and to clean brushes and paint spills. The gloss paints that are thinned with water are easier to use and to clean up after. Metal primers are: 1. calcium plumbate, which is an oil-based primer used on galvanised surfaces; 2. zinc chromate, which is an oil-based primer that is good for bare metal surfaces. Water-thinned paints form the bulk of paints today. They are less durable than gloss paints, but they are also easier to apply. Because they do not seal surfaces, you can use these paints on new plaster. Water-thinned paints have the primer, undercoat and finish in the same container. Two types of water-thinned paints are: limewashes; Z emulsions. Limewashes are made from hydrated lime mixed with water. They are a cheap way to apply a white finish to plaster and render, but they do not adhere v/ell and they brush or wash off easily. Emulsion paints are made from vinyl, acrylics and polyurethane in water. They dry quickly, leav¬ ing a matt, eggshell or gloss finish, depending on your preference. Emulsion paints can also be used as primer and undercoats on unpainted wood sur¬ faces. How to paint new woodwork with gloss paint Undercoats for gloss paints are modified gloss paints that dry with flat finishes. This makes it easier to rub them down and improves the adhe¬ sion of the gloss coat. Undercoats also fill in the colour over the primer and consolidate the final colour. Table 20.2 describes howr to paint new woodwork with gloss paint. Gloss paint is more complicated to use than other types of paint. A successful job depends on how well the surface is prepared. The background must be dry or else moisture will cause the paint to blister. 189 Finishes Table 20.2 How to paint woodwork with gloss paint How to paint plastered walls and ceilings Step Action 1 Rub down the wood in the direction of the grain with glass paper. Follow the steps in Table 20.4 when you paint smooth plaster on internal walls and ceilings. 2 Clean all dust and dirt from the surface. 3 Seal knots to prevent resin leaking through with a mixture of shellac and methylated spirits. Table 20.4 How to paint smooth plaster on walls and ceilings Step Action 1 Remove all plaster splashes with a scraper. 2 Fill in and rub down any holes, scratches or grooves. 3 Remove dust with a soft brush. 4 Dilute the emulsion with 10 per cent additional water and paint it on as a priming coat. 4 Seal the bare wood with a primer. 5 Fill holes and cracks with a plastic filler paste. 6 Rub the surface with glass paper to smooth the filler. .7 Brush on the undercoat. 8 Rub down with glass paper after the undercoat dries. It is optional to apply a second coat of undercoat. 5 Leave it about an hour. 6 Apply the full-strength emulsion. Brush on the gloss coat. 7 Leave it for 2 or 3 hours. 8 Paint on the final coat of emulsion. 9 How to paint metalwork with gloss paint Metals such as iron and steel should be painted to prevent corrosion. Unpainted metals must have a coat of primer first because the surface does not offer any suction. Because unpainted metals rust so quickly, they will often receive coats of primer in the factory to protect them while they are trans¬ ported. The only preparation is to remove any rust or grease before metal is painted with a primer. To paint metalwork you follow the steps in Table 20.3. Floor finishes Floor finishes for domestic buildings include a wide range of alternatives. The factors that may influence your choice depend on the use of the floor space and limits on cost. You need to consider a long list of characteris¬ tics when you select a floor finish. Resistance to wear Some parts of a building receive more use than others or are in closer contact with the dust or mud outside. The floor finish should match the type of wear that is normal in a specific part of a building so that it lasts many years without replacement. Resistance to grease and oil Table 20.3 Painting metalwork with gloss paint The floor should not be damaged by grease and oil spills and they should be easily wiped up from the surface. Spills are a particular problem in kitchens. Step Action 1 Remove any rust with wire wool and clean with white spirit to remove grease. 2 Paint dry metal with primer (not in damp, cold weather). A second coat of primer is optional. 3 Rub down the primer. 4 Brush on the undercoat. 5 Rub down the undercoat. Ease of cleaning 6 Brush on the gloss. Surfaces that allow dirt to easily penetrate are harder to keep clean. If ease of cleaning is a Resistance to water spills The flooring in bathrooms and kitchens needs to withstand water spills from washing or plumbing leaks. 190 Building construction priority, then a hard, smooth finish is better than a soft, open texture. Warmth or coolness Hard, smooth surfaces are cool to walk on because they conduct heat away. Soft, textured finishes like carpet give a room a warmer feel, which may be suitable for cooler climates. Noise Hard surfaces do not absorb sound so they are noisier than soft surfaces. Cost The costs vary enormously for the huge range of finishes. The cheapest finish is a cement screed. The most expensive can be carpet, wood block or special floor tiles. Wet cement finishes You can lay wet cement finishes to wet or dry subfloors. A wet subfloor is one where the con¬ crete subfloor has just been laid and is green (not fully cured) when the cement finish is applied. Monolithic screeds When wet cement is laid on a green subfloor it is called a monolithic screed. Monolithic means that the materials in the subfloor and the finish com¬ bine to become a single unit. This is a very good way to make a sound floor, but it is difficult to do because of the organisation needed to lay the concrete subfloor and the wet cement finish within a short space of time. Cement-based screeds Preparing a subfloor The subfloor for a floor finish will be concrete or timber, depending on the type of floor construc¬ tion. Most subfloors need to be prepared before you apply a finish. However, one alternative is to leave a subfloor as it is. If a concrete subfloor in a garage or storeroom is the finished floor, then it can be left rough or trowelled smooth. The timber boards of a suspended timber floor can also be left exposed and sanded and polished for a floor finish. One form of preparation is a cement and sand floor screed, trowelled to a smooth, hard finish, on a subfloor. The screed can be: 1. a floor finish; 2. a levelling screed between rough concrete and the final floor finish. A 3 mm hardboard base can be nailed over uneven timber floor boards as another type of preparation for a floor finish. Finishes on concrete subfloors The three main finishes for concrete subfloors are: 1. wet cement; 2. cement-based; 3. terra zzo. _ If the subfloor dries and hardens before the wet cement finish is applied, then the bond is only held in place by the weight of the screed. Bonded screeds need to be thicker and heavier than mono¬ lithic screeds. Cement-based finishes can be laid on monolithic or bonded screeds as: cement and sand screeds; granolithic screeds. You lay a cement and sand screed if the concrete subfloor is not smooth or level enough for a floor finish. The screed consists of a layer of mortar, which provides a good surface when levelled with a steel trowel. The thickness of the mortar, which does not give any structural support, varies from 25 to 60 mm in a 1:3 cement and sand mix depending on circumstances. As little water should be used as possible to minimise shrinkage. The screed should be laid in bays (small areas less than 9-10 m2). You use battens fixed by small mounds of mortar to divide the space and provide levels for the finish. A timber screed board that spans the battens can be used to spread and level the mortar before smoothing it with a steel trowel. You can see how to do this in Figure 20.4. A screed needs to be cured for seven days, like other cement-based structures. The bays of the screed should be in the same place as the bays in the subfloor. This reduces cracking if the subfloor moves. Granolithic screeds use granite chippings in a cement and sand screed in 1:1:3 mixes to improve Finishes the wearing qualities. The granite chips are graded from 5 mm to dust. This screed can be laid on fresh concrete so that it forms a 25 mm monolithic bond in bays which are less than 10 m2. If you lay the screed after the concrete is dry, then the thickness of the screed must be 40-50 mm. The top of the granolithic screed must be levelled and compacted. It becomes firm when it sets. In this state you must smooth it with a steel trowel at least three times in a 6 hour period to produce a hard, dense surface without an accumu¬ lation of fine particles. The screed must be cured for seven days. This is a difficult floor finish to produce, but it is extremely durable if it is done well. The most serious defect is the loss of contact with the subfloor around the edges of the bays. You should make the screed the maximum thickness to hold it firmly in position. Terrazzo finishes Terrazzo floor finishes came from Italy where 191 marble was abundant and used as a general build¬ ing material. White cement is the basis for the finish, but there is no sand in the 1:2 cement and marble mix. You make the aggregate by breaking marble into 2-25 mm pieces. The marble chips in a floor should all be about the same size. A typical floor will have marble chips that are 3-6 mm. If you use the smaller marble chips, then the cement and marble are mixed together and laid as one finish. The alternative is to mix cement and marble dust and then place larger pieces of marble one by one into the mixture. The thickness of the terrazzo depends on the size of the aggregate. The standard thickness is about 15 mm. You lay a terrazzo floor by applying a 25 mm cement and sand screed which is followed by the cement and marble mixture while the screed is still fresh. Table 20.5 describes how to lay a terrazzo finish to a dry subfloor, because it is extremely difficult to lay it as a monolithic bond. 192 Building construction Table 20.5 Laying a terrazzo finish Step Action 1 Pour the terrazzo into bays separated by metal strips. 2 Consolidate and compact the mixture with a roller. 3 Smooth the mixture with a steel trowel and leave it to harden. 4 Grind the surface with a rough paste to make a smooth finish. 5 Wash and buff with a polisher. An important feature of a terrazzo finish is the use of metal, ebonite or plastic strips which go through the screed to the subfloor to divide it into bays. The purpose of the strips is to limit the bays to 1 m2. This prevents shrinkage cracks and makes the floor finish particularly decorative if different colours of terrazzo are used. Figure 20.5 A wood mosaic floor finish. Wood finishes on concrete subfloors The two most common wood floor finishes are: 1. wood mosaic; 2. wood strip. Wood mosaic is a low-cost type of hardwood floor that uses offcuts of hardwood. The wood is shaped into pieces 150 x 300 x 10 mm and assem¬ bled into 300 x 300 x 10 mm panels. The panels are laid in groups of five in a basket weave pattern on a paper backing which holds them together while they are transported. Figure 20.5 shows you an example of a wood mosaic floor. You lay each panel separately on a completely dry cement and sand screed. First, you clean the screed to remove any dust and loose material. You then stick the panels on the screed with adhesive so that each panel fits tightly against the next one. There should not be a joint showing between 193 Finishes Figure 20.6 Wood strip flooring nailed to joists or battens. them. You complete this floor finish by removing the paper backing, sanding the surface to a smooth finish and polishing. Wood strip flooring is made from timber strips in softwood or hardwood fixed to battens on a concrete subfloor. The battens are secured by: 1. casting galvanised metal clips into the concrete or screed; 2. casting dovetail battens into the screed so they are anchored as the screed dries. The method for fixing a timber floor finish is similar to fixing a suspended timber floor. You complete the process by sanding and polishing to a fine finish. Figure 20.6 is a plan of wood strip flooring. Laying tiles on concrete subfloors Tiles are made from a variety of materials and laid on a subfloor in individual units to form a com¬ plete covering. They are laid on an adhesive or mortar bed, depending on the tile material. Some tiles have wide joints, which have to be filled separately, while others are fitted so tightly that no joint filling is needed. This section looks at laying PVC and quarry tiles. PVC tiles have precise measurements (300 x 300 x 3 mm). They must be laid on a perfectly smooth screed because they are so thin and fixed with adhesive. However, they can be fitted so closely that they do not have a gap in the joints. See Figure 20.7 to see what a section of floor laid with PVC tiles looks like. PVC tiles are usually: resistant to grease and oil; waterproof; durable. Although they come in a wide range of colours and textures, PVC tiles are one of the cheapest floor finishes you can buy and lay. They are main¬ tained by applying a surface coating of wax and then washing with soapy water. Quarry tiles are clay tiles with a hard semiglazed finish. They usually measure about 150 x 150 mm or 100 x 100 mm and are 15-20 mm thick. Since they are fired in a kiln they are not shaped as precisely as PVC tiles, so they have a 3 mm joint between the tiles. Quarry tiles are bedded in mortar so a levelling screed is not usually necessary. The level of the finished floor is determined by battens, which are 194 Building construction Figure 20.7 A section of floor laid with PVC tiles. Figure 20.8 Fixing quarry tiles. Finishes the thickness of the tile, fixed temporarily to the floor and levelled (Figure 20.8). The bedding should be a 1:10 mix of cement and sand mortar. You spread the mortar on the concrete and bed the tiles level to the battens. The joints should be grouted with a 1:1 cement and sand grout. 195 filling with white cement, called grout. You can use matches to space tiles that do not have lugs. Common sizes for wall tiles are 150 x 150 x 5-6 mm 100 x 100 x 4-5 mm Their shapes and sizes may vary, but the meth¬ ods of fixing and pointing are the same for all tiles. Finishes on timber floors It usually is not practical to lay any cement-based finishes on timber floors. Because timber moves and flexes, it is liable to cause cracks in the floor finish. The added weight of a cement-based finish would also mean that the floor construction would have to be heavier and stronger. The finishes that can be laid on timber floors are: 1. PVC tiles, which can be laid on the flooring as long as the boards are flush at the joints. It is safer to lay a 3 mm hardboard cover over stand¬ ard 100 mm strip flooring to avoid the joints showing through; 2. carpet, which can be from a wide range of qualities and styles. An underlay will protect the carpet and extend its lifespan. You can lay car¬ pet loosely as squares and rectangles, fit it from wall to wall in seamless areas or lay carpet tiles on adhesive backs. Wall tiling For centuries, tiles have been a good material to make smooth, hygienic and decorative surfaces. They are easy to clean and last indefinitely with normal use. Tiles are made from clays with special additives. The clay is ground to a fine powder and mixed with water to make a slip (a creamy paste). The water is extracted and the residue is dried and crushed. The resulting dust is moistened and pressed into the shape of a tile. The tiles are fired by putting them into a kiln at high temperature which sets the clay hard. Finally, a glaze is applied to the surface and the tile is fired again to bond the glaze to the unfinished tile. Modern tiles come in exact measurements so that it is easy to set them out on a wall. They may have small lugs or projections on the edges to space them accurately so that a 2 mm gap is left for Types of tile Square tiles are the most popular. They come in three varieties to suit the exposed ends of tile runs. The basic tile, which is glazed on the surface only, has unglazed edges. The surface of the basic tile can be: 1. slightly rounded near the edges. This is a cushion-edged tile; 2. rounded on one edge; 3. rounded on two edges. Fixing tiles to even surfaces The thin bed method for fixing tiles uses a special adhesive 1-2 mm thick to fix thin tiles to a smooth surface such as plaster. It can only be used on very smooth surfaces since the adhesive is the only anchor for the tiles. You should plaster an entire room and then stick the tiles on instead of plaster¬ ing a small area for fixing tiles first. Fixing tiles to uneven surfaces If the tiling has to be fixed to an uneven surface, then you may want to use the thick bed method. You prepare a 1:4 cement and sand mortar and spread it over a wall as a wet bed to push the tiles into. As a guide to the finished levels, you can nail battens to the wall which are the same thickness as the tile and mortar bed. Tiling techniques To produce good tiling you need to know how to: 1. level; 2. cut tiles; 3. set out and measure; 4. fill joints. Levelling Tiling joints should be perfectly horizontal and vertical. Since the tiles are usually square you only need to level the horizontal edges. You begin by drawing a line on the wall using a level above a fitting like a sink or bath. You fix the first row of 196 Building construction tiles so that their bottom edges are level with this line. If there is no fitting, then you fix and level a batten on the wall to be a guide and to support the tiles while the adhesive or mortar sets. You should continue to check the horizontal levels as you work. Cutting tiles You need a glass cutting tool or special tile cutters to cut through a glazed tile surface. If you need a piece of tile to finish off a row, then follow these steps: 1. Measure the space and deduct 4 mm to allow for two joints. 2. Cut a line into the clay part of the tile using a straight edge as a guide to the correct measure¬ ment. 3. Lay the tile on a batten so that the cut line is over the edge of the batten. 4. Press down on each side of the line so that the tile breaks cleanly. Setting out and measuring You use this technique to decide where to put a piece of tile if the row is not an exact multiple of the number of tiles. Example Each tile is 150 mm wide. You need a piece of tile 100 mm to complete a row. It could be fixed in the centre with full tiles on either side or you could cut two 50 mm pieces for each end. An area of tiles looks better if cut tiles are in the bottom row and full tiles are above. Making joints All joints have to be filled when you complete the tiling. You use a special white grouting material which is moisture-resistant and flexible enough to allow small movement in the tiles. You spread the grout over the tile surface and work it into the joints with a damp sponge. You finish by wiping off the surplus and polishing the tiles with a dry cloth when the grout is hard. CHECK YOUR UNDERSTANDING Plastering and rendering provide even, hard finishes to internal and external brick and block walls. Plaster is usually made from lime or gypsum. Render is usually cement-based. Plaster may have to be applied in one, two or three coats, depending on the type of surface and how even it is. Plasterboard is a good background surface for timber ceilings and pitched roofs. Masonry background surfaces should be wetted to prevent suction from the plaster mix. Paint is decorative and protective. Paint consists of binders, pigments and thinners. Screeds can provide a level surface for the floor finishes. Wet finishes on concrete floors are usually cement-based. Wall tiles provide a smooth, durable and waterresistant surface for kitchens and bathrooms. REVISION EXERCISES AND QUESTIONS 1 Why do you plaster walls and ceilings? 2 What do these words mean: i) key ii) suction? 3 How do you fix plasterboard on a timber ceiling? 4 How do you prepare a wall for a backing coat of plaster? 5 How do you prepare and paint external timber? 6 How do you apply a bonded screed to a con¬ crete floor? ology Introduction In previous chapters you read about using con¬ crete to make foundations, floors, stairs and roofs. Because concrete is such an important part of a building’s structure this chapter looks at how to produce it in more detail. The general principles are that you mix cement, sand and aggregates with water. The cement ab¬ sorbs the water in a chemical process called hydration so that it binds the sand and gravel into a tough, hard mass. Surplus water in the mixture gives the concrete enough pliability to flow and be levelled and compacted. When the surplus water evaporates, then the concrete sets and hardens into shape. Materials used to make concrete The main materials in concrete are: cement; sand; aggregates; water. Cement Cement (often called Portland cement) is a com¬ bination of limestone (calcium carbonate) and silica, which is found in some types of clay. Alumina, iron oxide and magnesia are present in small quan¬ tities. The cement may also contain calcium sul¬ phate to extend the setting time. Tests to ensure the quality of the cement are available, but they are not usually carried out on site. Because cement is normally manufactured to such a high standard, you should be able to trust its quality when you buy it. You usually buy cement in 50 kg bags for small jobs. You must store it in a dry place such as a small lockable shed. You should take these precautions on site to ensure that you use cement which is in excel¬ lent condition: Check the date on the bag to see that it was manufactured recently. Cement deteriorates over time. Store the bags of cement on a timber base so that they do not rest on the ground. Cover the bags with a waterproof sheet. Do not stack the bags too high or the pressure from the upper bags will com¬ press the cement in the lower bags and spoil it. Use the cement in the order that you re¬ ceive it on site to make sure it does not become stale. Sand Sand is the fine aggregate in concrete mixtures. You should use sand from rivers and quarries. If you use sea sand, then you should wash it thor¬ oughly to remove the salt, which contains sul¬ phates that can attack cement. The sand must also be free from excessive silt or other impurities. 197 198 Building construction You can carry out a silt test to check that there is less than 5 per cent silt in the sand: Place a sample of sand in the bottom of a measuring flask. Add water to the top of the flask. • Shake the flask and allow it to stand for a few hours. • Measure the amount of silt and sand that settles to the bottom (the silt will be a dark band on top of the sand). • Calculate the percentage of silt. Aggregates The coarse aggregates in the concrete mix have individual pieces which are more than 5 mm in diameter. Typical sizes are: 5 mm 10 mm 20 mm 38 mm You make aggregates by crushing rock such as granite, sandstone, close-grained limestone or gravel which you obtain from river beds, quarries or the seashore. Good aggregates should be: 1. clean, so that the cement can adhere to them; 2. strong enough to produce the final strength of the concrete; 3. durable enough to resist extremes of heat and cold; 4. inert in the presence of water. Water Water for construction work should be as clean as tap water. River water may contain soluble salts that can spoil the concrete, so you should analyse samples before use. You may need to organise tankers to deliver the water to the site at suitable intervals. This water should be stored in covered containers. Concrete mixes Tables 21.1-21.6 show you the most common mixes for different volumes of concrete and for different parts of concrete structures. Table 21.1 Volume of concrete produced from 50 kg cement Mix Volume of concrete 1:3:6 0.24 m3 1:2:4 0.17 m3 1 :.5:3 0.13 m3 Table 21.2 Quantity of materials required to produce 1 m3 of concrete Mix Cement (kg) Sand (m3) Aggregate (m3) 1:3:6 172 0.36 0.72 1:2:4 238 0.33 0.67 1: .5:3 299 0.13 0.62 Table 21.3 Approximate volumes for buckets Mix Cement (buckets) Sand (buckets) Aggregates (buckets) Water (buckets) 1:3:6 1 3 6 0.75 1:2:4 1 2 4 0.5-0.75 1 :.5:3 1 0.5 3 0.5 Table 21.5 Water and cement ratio for normal slump Mix Water and cement ratio Litre of water for 50 kg cement 1:3:6 0.7 36 1:2:4 0.55 27 1 :.5:3 0.5 25 Table 21.4 Mixes for different concrete structures Mix Structure Cement (kg) Sand (m3) Aggregate (m3) Water (litre) 1:3:6 Mass foundations Oversite slabs 50 0.11 0.212 (25 mm) 36 General reinforced concrete work 50 1:2:4 ■v 0.07 0.143 (15 mm) 30 Concrete technology Table 21.6 Maximum slump for concrete structures Concrete structure Maximum slump (mm) Mass foundations 76 Reinforced foundations 100 Oversite concrete 125 Reinforced slabs and beams 125 Reinforced columns 100 This section describes the standard mixes and how to make them using approximate measure¬ ments. Figure 21.1 describes this process graphi¬ cally as well. Strip foundations, which are mass concrete, are mixed by volume in the following propor¬ tions : 1 part cement 3 parts sand 6 parts aggregate Making concrete by volume Standard mixes are usually successful for small jobs. To make sure that you put the correct quantities in the mixer, you should make a gauge box for 25 kg cement. ? 1 volume of cement/0.035 m3 / p 199 ? XrtV.iM 71 3 volumes of sand/0.105 m3 / 6 volumes of coarse aggregate/0.21 m3 Mix = 1:3:6 Figure 21.1 Making concrete by volume. 200 Building construction Example A 1:2:4 mix is 1 volume cement 2 volumes sand 4 volumes aggregate Cement weighs 1442 kg/m3 so 25 kg has a volume of: = 0.017 m3 1442 For large quantities of concrete, it is easier to weigh the amounts before placing the materials in a mixer. This method offers greater control over the quality of the concrete if strength and pliability are important. The standard weights of materials are If you make a gauge box which measures 350 x 200 mm, then the depth will be: —2^12- = 0.243 m 0.35 x 0.20 (say 250 mm) To measure the ingredients for a 1:3:6 mix for a small mixer, you should use the example in Table 21.7 as a guide. Weight (kg) Volume (m3) Cement 2 50 0.04 Sand 6 168 0.11 Aggregate 12 302 0.21 1442 kg/m3 1600 kg/m3 1440 kg/m3 You need to calculate the quantity of materials that will fit into a large mixer by converting the volumes into weights as shown in Table 21.8. The mix ratios are based on a 50 kg bag of cement in a 1:2:4 mix. A mixer with a volume of 0.300 m3 can take the volume of 0.27 m3 as you calculated in Table 21.8. You can increase the amounts to completely fill the mixer by multiplying the weight of the materials by 1.1 (0.300/0.272). Table 21.7 Volume of ingredients for a 1:3:6 mix Material (boxes) cement sand aggregates Table 21.5 shows you that this mixture requires 36 litres of water, which increases the total volume of ingredients to 0.386 m3. During the mixing pro¬ cess the bulk volume increases so that this mix produces 0.24 m3 wet concrete (Table 21.1). If this batch is used for strip foundations that are 600 x 200 mm, then it is enough for a 2 metre long strip. The weights of materials required to fill a 0.300 m3 mixer are cement sand aggregate water 50 kg x 1.1 = 55 kg 112 kg x 1.1 = 123.2 kg 201.6 kg x 1.1 = 221.76 kg 27 litres x 1.1 = 29.7 litres How to weigh the materials Volume of materials You can choose from two methods to weigh the materials: You usually define a concrete mix by the volume of materials required. 1. using a concrete mixer; 2. using a separate weigh-batcher. Table 21.8 Converting volumes to weights Material Mix ratio (volume) Volume (m3) Weight (kg) Cement 1 50/1442 = .035 50 Sand 2 0.07 1600 x .07 = 112 Aggregate 4 0.14 1440 x .14 = 201.6 Water 27 0.03 Total volume 0.27 Concrete technology A concrete mixer may have a scale attached to weigh materials as they are put into a hopper. A dial on the mixer allows you to measure the amounts. After the hopper is loaded, then the materials slide into the mixer and a valve opens to feed the correct amount of water into the drum. A separate weigh-batcher also has a scale with dials that you can read to measure the correct amounts as you add them. The weigh-batcher is placed near the mixer so that its hopper can tip the materials into the drum of the mixer. The correct volume of water is added directly to the mixer. Adjusting the water content of damp sand Wet sand increases in volume by up to 25 per cent, depending on the amount of water present. This is called bulking. When you use wet sand to make concrete you must consider how much to: 1. adjust the volume of a batch to ensure that you add the correct amount of sand; 2. reduce the amount of surplus water. You can follow these steps to measure the water content in sand: Weigh 1 kg of wet sand in a fireproof container (remember to weigh the con¬ tainer). Heat the container over a fire to remove the water. Weigh the sand and container again to see if the sand weighs less. Check the reduction in volume. If the sand weighs 0.85 kg, then it contained 0.15 kg (0.15 litres) of water. When you make concrete with this wet sand, then you need to increase the amount of sand by 15 per cent and adjust the amount of water that you add. 201 is to calculate how much to adjust the sand and water mix. When you measure the water content in the sand you find that each box of wet sand contains 2.5 litres of water. The bulking is 15 per cent of the volume of dry sand. The mix requires these quantities of materials: 50 kg cement or 2 gauge boxes 302 kg aggregate or 12 gauge boxes 168 kg sand or 6 gauge boxes of dry sand Each gauge box should contain 27 kg of dry sand when full. Because of the water in the sand, the boxes contain 22.95 kg dry sand (27 kg x 85 per cent). Follow these calculations to find out how much sand and water to adjust in the mix: 1. 22.95 kg x 6 gauge boxes = 137.7 kg of dry sand. 2. Add 1.3 gauge boxes of wet sand to make up a deficit of 30.3 kg of dry sand (168 kg - 137.7 kg = 30.3 kg). 3. This totals 7.3 gauge boxes of wet sand for the mix. 4. 7.3 gauge boxes contain 18.25 litres of water (7.3 boxes x 2.5 litres = 18.25 litres). 5. Subtract the surplus water from the water re¬ quired for the mix (36 - 18.25 litres). 6. The total amount of water to be added to this mix with wet sand = 17.75 litres. Summary The mix should consist of these proportions: 2 boxes of cement 7.3 boxes of sand 12 boxes of aggregate 17.75 litres of water Grading coarse aggregates Grading means selecting the size of stone particles to suit the type of concrete you produce. You can select the aggregate by passing it through mesh sieves with wires spaced for specific sizes of stones. Example The following example shows you how to adjust the amount of water in the mix. Example You want to make a concrete mix of 1:3:6 by volume. You know from Table 21.5 that a 50 kg bag of cement requires 36 litres of water. The task If a sieve has 10 mm gaps in the wire mesh, then only stones 10 mm and bigger will stay in it. Smaller stones fall through the holes. Sieved aggregate is single size aggregate. Con¬ crete made with single size aggregate has large spaces between each stone, which can be filled 202 Building construction with sand to remove air pockets, which could weaken the mixture. To make strong, dense concrete you need to grade the aggregate. This means that you need a range of different sizes of stones to fit together and fill in the spaces. When you order you can ask for 10 mm gradeci aggregate which will ensure that you get a suitable mixture of the right size stones for the type of concrete. A structural engineer can determine the correct size and grading of aggre¬ gate for the building project. Push the wheelbarrow carefully so that you do not spill the contents or cause the cement to separate from the aggregate. This could affect the strength of the concrete. Similarly, when you pour the concrete, you should not tip it more than a metre from the barrow to the formwork. Bring the lip of the barrow closer to the ground if the concrete has a long drop. Compacting concrete Moving concrete After you mix the concrete, then you must move it to the location for pouring it. The mixture should be firm enough so that it does not slop around and spill while it is being moved in a wheelbarrow. You should lay a line of boards to make a firm surface for pushing a wheelbarrow. A loaded barrow can be extremely difficult to push over soft spots and obstructions. Concrete has to be compacted to remove trapped air after it is poured into position. Air can form cavities in the concrete, which reduces its strength. You can compact by tamping the concrete steadily with a steel bar, but a mechanical vibrator is more efficient. If the concrete contains reinforcement you have to use a vibrator to ensure that the concrete flows around the steel bars and into the corners of the formwork. After you compact concrete, then you should level the top with a screed board so that it is level with the pegs on the formwork. Gap to allow moisture to escape Figure 21.2 Curing concrete with polythene sheets. Concrete technology Controlling moisture loss Concrete dries quickly in hot weather. You need to control the rate of moisture loss to: 1. retain water for hydration; 2. slow down shrinkage. The standard method for controlling moisture loss during the hardening and maturing process is to cover it with polythene sheets or wet sacks. Polythene traps moisture so that it evaporates very gradually. You can see how to do this in Figure 21.2. You need to spray sacks with water at regular intervals to keep the concrete moist. These meas¬ ures are necessary during the seven day curing process. The most experienced workers on site will be able to judge when the wet concrete flows cor¬ rectly. Table 21.6 gives you some standard meas¬ urements for the slump for different concrete structures. The compression test The compression test is another test for concrete. You take a sample cube of concrete that measures 150 x 150 mm and let it cure and harden for 28 days. It is then crushed in a laboratory to assess its strength. If the test sample fails to reach the required strength, then some of the concrete work Testing concrete and its materials The ratio of cement to water has the greatest effect on the strength and durability of concrete. The concrete must be wet enough to flow into all parts of a structure, whether it is formwork for a slab or an excavation for a strip foundation. At the same time, the water content must be kept to a minimum to achieve a full-strength concrete. The best method for testing for the correct amount of water in the mixture is to use the slump test which is described in Table 21.9. Unconfined wet concrete slumps or sags so a test has been devel¬ oped to measure the amount of slump. You need this equipment for a slump test: • special metal cone; # tamping rod; measure. Table 21.9 How to do a slump test Step Action 1 Put mixed concrete in a metal cone on a flat base. 2 Pack it down layer by layer with the tamping rod until the cone is full. 3 Level the top with a steel trowel. 4 Remove the cone and the concrete will sag (slump). 5 Measure the distance from the top of the cone to the top of the slumped concrete. Compare this with the desired level of slump. 6 Increase or decrease the water in the mix to get the correct slump. 203 Figure 21.3 Testing concrete in a laboratory. 204 Building construction may have to be done again. Figure 21.3 shows you the equipment in a concrete testing laboratory. Reinforcement in concrete Steel reinforcement bars, which are made from mild steel, are used to resist the tension forces in concrete. They also control shearing in beams. You can see a variety of reinforcement bars in Figure 21.4. The thinnest bars, which are used for making stirrups to hold other bars in position, are 6 mm in diameter. Reinforcement bars range in diameter from 10 mm to 25 mm. Other bars, which are called deformed bars, are made with patterned surfaces to increase the bond between the steel and the concrete in highly stressed conditions. Mesh fabric is another type of reinforcement used in ground-floor slabs or heavy road construc¬ tion. It consists of 5-12 mm steel wires welded together in a square or oblong pattern. The heavier mesh comes in flat sheets, but the thinner mesh is supplied in rolls. The bond between the steel bar and concrete is important. The bar must be so secure that it cannot move within the concrete. You can bend reinforce¬ ment bars into right angles in conditions of low stress or hook them on their ends to anchor them. The bends or hooks have specific dimensions to retain the structural integrity of the bars. The distance between the reinforcement bars and the concrete surface is also important. This distance is called the cover. The purpose of the cover is to: 1. protect the steel from corrosion due to atmos¬ pheric moisture and rain; 2. protect the steel from corrosion due to poor compaction or segregation; 3. provide enough concrete to make a good bond; 4. insulate the steel from early failure in a fire. The formula for the minimum reinforcement cover is: It should be twice the diameter of the bar, and at least 25 mm. If the concrete is exposed to rain, then the cover must be more than 40 mm. Concrete mixers A simple petrol-driven, tilting-drum mixer is ad¬ equate for small jobs. The capacity of mixers is measured in litres. This indicates the capacity of the mixing drum and the amount of wet concrete it can produce. Example If the total volume of ingredients is 0.35 m3 and it produces 0.24 m3, then you need a 400/300 litre model. It has a capacity of 0.4 m3 and an output of 0.3 m3. Another standard size mixer is the 300/200 model. The mixing process, including loading and discharging the concrete, takes from 3 to 5 minutes. You load the cement and aggregates into the mixer drum as it rotates. Then add the correct amounts of water until the contents are completely mixed. You tilt the drum the other way to pour the concrete into a wheelbarrow or dumptruck. Mixing concrete by hand You measure out the dry ingredients by volume and mix them on a clean, hard surface (not on the ground). Then make a depression in the middle of the dry ingredients and add a measured quantity of water. Mix the ingredients again and continue to add the rest of the water slowly until the concrete has an even appearance. To test the quality of the mix, you should draw a shovel backwards through the concrete to leave grooves and ridges. If the mix is too dry, then the ridges will crumble. If the mix is too wet, then the ridges will slump. CHECK YOUR UNDERSTANDING •v Concrete is a mixture of cement, sand, aggre¬ gates and water. Wet concrete is pliable, but it hardens when it dries. Concrete technology Plain: mild steel Ribbed: high tensile steel Figure 21.4 Reinforcement bars. 205 206 Building construction Concrete mixes vary according to the strength required. Aggregates are normally graded according to the type of structure being built. C Concrete can be made in batches according to volume or weight. C A slump test is a means of finding out how well you can work the concrete for specific structures. The water content in sand affects the strength of the concrete. Concrete must be well-compacted. © Steel reinforcement resists tension and shear forces. Reinforcement must have enough cover. < Concrete must be transported carefully to pre¬ vent segregation of the cement and aggregate. REVISION EXERCISES AND QUESTIONS 1 2 3 4 5 6 What is the purpose of w ater in a concrete mix' W hat precautions should you take when you store cement? Describe how to test for silt. What do these words mean: 0 graded aggregate ii) bulking of sand iii) slump? If you plan to use a 1:2:4 concrete mix with 30 litres of water, then calculate the quantities of materials you need to make 3 m-' concrete using a 2^ kg gauge box. How do you check the moisture content of sand? Introduction The soil that supports a building is called the natural foundation. The artificial foundation constructed from concrete is built on the natural foundation. Everything that goes into the construction of a building and everything that goes into a building exerts a load on the soil. This chapter describes the factors that you should be aware of during con¬ struction such as: The ability to support a load is called the bear¬ ing capacity. The bearing capacity is defined as the load that a unit area of soil can safely support. The load that is imposed on the soil is called the bearing pressure which must not be greater than the bearing capacity of the soil. An artificial foun¬ dation should be constructed with a 10 per cent safety margin to ensure that the soil can bear the pressure from the loads. Table 22.1 shows you typical bearing capacities for different types of subsoil. 1. the load-bearing capacity of the soil; 2. the type of soil; 3. the correct foundation for the soil type. Load-bearing capacity The structure of a building is called the dead load. The people, furniture and fittings which go into a completed building are the live or superimposed loads Do you remember from Chapter 7 that you remove the topsoil before you build the foun¬ dations? This exposes the subsoil. Table 22.7 Soil bearing capacities Type of subsoil Typically, building regulations state that the building foundation must safely sustain and transmit to the ground the combined dead, imposed and wind loads so that there will be no settlement or movement that could impair the stability of the building. In Chapter 5 you read about digging trial holes as part of the initial site investigation to find out about soil conditions. The building designer then selects the type of foundation that is appropriate for the proposed loads and the soil. Soil bearing capacity (kN/m2) Rock 600-10 000 Compact gravel and sand 300-600 Stiff clay 200-400 Soft clay 50-100 Loose gravel and sand 75-200 Very soft clay and silt 00-75 ■ Classifying soils Soils can be classified according to the size of their particles, as you can see in Table 22.2. 207 208 Building construction Table 22.2 Soil particle size Subsoil type Particle size (diameter in mm) Rock Does not apply Gravel Larger than 2.0 Sand 0.06-2.0 Silt 0.002-0.06 Less than 0.002 Soil can also be classified by its cohesive quali¬ ties. Cohesive soils have particles that stick to¬ gether more easily. Non-cohesive soils have particles which do not stick together and remain separate. Cohesive soils are: The amount of water in the soil affects the cohesive qualities of soil types. When cohesive soils are pressed under loads, then they compact and settle. Non-cohesive soil types compress only slightly under a load because they do not contain much water. Choosing the right foundation The guidelines in Table 22.3 will help you to test soil types for a foundation. • silt; • clay. Non-cohesive soils are: • gravel; # sand. Figure 22.1 Loading on a strip foundation from a one-storey building. Figure 22.2 Loading on a strip foundation from a two-storey building. 209 Soil technology You can build a one-storey house in firm, sandy clay which requires a minimum strip foundation which is 300 mm wide (Figure 22.1). The bearing pressure is 25 kN/per metre run. This makes a bearing pressure per square metre of Since the foundation is square, the length of one side would be Vl.346 or 1.160. For practical pur¬ poses this makes a pad foundation that measures 1200 x 1200 mm. CHECK YOUR UNDERSTANDING 1/0.3 x 25 = 83 kN/m2 For a two-storey house built on silty sand, the minimum width foundation would be 600 mm (Figure 22.2). The bearing pressure per square metre would be 1/0.6 x 33 = 55 kN/m2 Bearing capacity for pad foundations A concentrated load may be supported by a col¬ umn or free-standing brick pier on a pad founda¬ tion. The size of the foundation should be related to the load carried by the pier and the soil bearing capacity. Example The bearing pressure for a brick pier that supports the load from part of the upper floor, wall and roof of a two-storey building is 70 kN. The soft clay ground has a bearing capacity of 52 kN/m2. Area of foundation in m2 = bearing pressure in kN/bearing capacity of soil in kN/m2 = 70/52 = 1.346 m2 The soil’s ability to support a load is its bearing capacity. The load on the soil is the bearing pressure. Soil is a natural foundation for a building. The soil must support the dead weight of a building without subsiding. Trial holes are used to investigate soil condition. Soils vary widely in their bearing capacity. Soils can be cohesive or non-cohesive. Pad foundation sizes are determined by the formula area of foundation in m2 = bearing pressure in kN/bearing capacity of soil in kN/m2 REVISION EXERCISES AND QUESTIONS 1 2 3 4 5 What is the main difference between cohesive and non-cohesive soils? Which loads are supported by a natural foun¬ dation? What types of soil are poor for building on? Why should you dig trial holes? What size foundation do you need for a column with a bearing load of 118 kN on soil with a bearing capacity of 48 kN/m2? Table 22.3 Testing soil types for foundations Type of subsoil Consistency Testing methods Minimum width of strip foundation (mm) 25 kN/m 33 kN/m one-storey two-storey Rock Hard (sandstone or limestone) Requires mechanical excavation Width of wall Gravel and sand Compact Requires a pick to break up and pegs hard to drive in 250 300 Clay Stiff Requires pick and cannot be moulded by hand 250 300 Sandy clay Firm Requires spade and can be moulded by hand 300 350 Sand Loose Silty sand Can drive pegs in 400 600 Clay and silt Soft Can be easily moulded 450 650 Introduction Softwood and hardwood trees Timber has been a source of building material since people left the shelter of caves to live in open countryside. When we cut down trees for timber for building we should continuously re¬ place them in a planned programme of replanting. The more we know about the properties of trees, the easier it is to put the knowledge to good use to protect the environment. Some species grow more quickly than others. Fortunately for the environment, the quick¬ growing varieties are the bulk of our building timber. The two main types of tree are the softwoods and hardwoods. This chapter will describe the main features of these types of tree as well as the general characteristics of building timber. Softwood trees are also called coniferous or ever¬ green trees. Their main features are: 1. They have an open grained texture, which is easier to work on than hardwood. 2. They have a lighter colour than hardwood. 3. They do not shed their leaves seasonally. 4. Their leaves are usually needle- or cone-shaped. 5. They grow quite quickly. 6. They can be grown in plantations to provide a continuous supply of timber. 7. The timber they provide needs to be protected from the weather by paint, varnish or preserva¬ tives. 8. They need to be protected from insect attack (on the structural timbers). Bark Pith Heartwood Sap wood Medullary rays Figure 23.7 The parts of a cut tree. 210 Timber technology 211 Figure 23.2 An overview of turning a tree into timber. Cedar is an exception to these typical features of softwood trees. It is a broadleaf tree that is very resistant to rot and insect attack. It is commonly used for fence posts. 3. outer lighter-coloured concentric rings of woody tissue called sapwood; 4. lines which radiate from the centre called medullary rays. Each season a living tree adds alternate rings of heartwood and sapwood. Hardwood trees are the broadleaf trees, which grow more slowly. Their main characteristics are: 1. They are harder to work with hand tools than softwood trees. 2. They are darker in colour or have distinctive colours. 3. They shed their leaves seasonally. 4. They are slow growing and cannot be culti¬ vated. 5. They are more expensive to use for timber. 6. They are selected for their decorative appear¬ ance. 7. They are usually left undecorated except for varnish or polish. The structure of timber When you examine the cut end of a tree trunk you can see the parts shown in Figure 23.1: 1. a central core of woody tissue called the pith; 2. inner concentric rings of woody tissue called heartwood; How a tree grows A tree absorbs moisture and nutrients from the ground through its roots. This material rises to the leaves where it is converted by photosynthesis to sap, which is the growth material of the tree. New growth takes place in the last layer of the trunk and the outer bark. In a mature tree the inner part of the trunk hardens and carries no sap while the outer rings carry the sap. Seasoning timber Seasoning is the term that describes the changes in timber from the time a tree is cut down to its use in the construction of a building. After a tree is cut down (or felled), then it is made into timber by sawing it into planks. Figure 23.2 shows you an overview of this process. The timber is then pre¬ pared for drying out or seasoning. The moisture contained in the living tree evapo- 212 Building construction Figure 23.3 Storing timber for air-seasoning. Figure 23.4 Drying timber in a kiln. rates when the wood is cut into timber. The mois¬ ture loss should be controlled to avoid excessive shrinkage and distortion. The aim is to reduce the amount of moisture in the wood to an equilibrium with the moisture in the atmosphere. Timber should shrink slightly in its width and thickness, but not in its length. Timber continues to shrink and expand with changes in the moisture in the atmosphere. Natural seasoning After timber is cut into planks, it is stacked in open sheds and left to dry out naturally (Figure 23.3). This may take several months. Artificial seasoning Timber is seasoned artificially in a kiln like the one in Figure 23.4, which is an enclosed container with a temperature control. You put the timber in a kiln and blow warm air into it to evaporate the mois¬ ture until the timber reaches the required moisture content. This process takes one or two weeks. Timber technology Calculating the moisture content For stability, timber should have a 20 per cent moisture content, which is close to the moisture in the air. You measure the moisture content as the per¬ centage difference between a completely dry piece of timber and a similar piece containing moisture when you weigh the two for comparison. If you cut a piece of timber off a plank and weigh it, then its weight will be its own weight, plus the weight of any moisture in it. You then put the piece of timber in a kiln and heat it until its weight does not reduce any further. This means that all excess moisture has evaporated. 213 2. tangential sawing; 3. slab sawing. The choice of methods depends on the relation¬ ship between the rectangular shape and the growth rings of the tree. Radial sawing is also called rift or quarter saw¬ ing. You first cut the log into four pieces. Each piece is then sawn parallel to the radius into planks. The growth rings should fall across the width of the plank. Tangential sawing divides the tree into planks that are curved along an angle. The growth rings curve along the length of the planks. Slab sawing is sawn straight through to pro¬ duce tangential and radial sawn timber. The formula for calculating the moisture content is: Weight of sample with moisture - dry weight ^ Dry weight Example A piece of timber weighs 132.5 g Its dry weight is 108.7 g The moisture content weighs 23.8 g The percentage of the moisture content is (23.8/108.7) x 100 = 21.9 per cent Making timber from trees A tree is sawn into rectangular pieces using one of three methods, which you can see in Figure 23.5: 1. radial sawing; Warping is the change in shape from the orginal sawn shape of timber because of moisture loss. The most shrinkage occurs along the direction of the growth rings. There is also a small amount of shrinkage in the radial direction. Preserving timber Timber should have two types of preservative applied: 1. treatments to resist attack by rot fungus and wood-eating insects; 2. treatments such as paint, polish or varnish to protect it from moisture and pollution. Timber to be treated with preservative should Figure 23.5 Three common patterns for sawn timber; (a) radial sawn timber; (b) tangential sawn timber; (c) slab sawn timber. 214 Building construction be cut, shaped and prepared in advance of the building work. Any cutting afterwards exposes un¬ treated timber, which must have liquid preserva¬ tive applied by hand. You can use two methods to treat timber: 1. pressure impregnation; 2. steeping or immersion. Pressure impregnation is a method whereby you put the timber in a kiln or other container and create a vacuum inside by pumping out the air. You use pressure to force the preservative deeply into the timber. You then adjust the moisture con¬ tent and remove the timber. Steeping or immersion is a method where you put the timber in a tank filled with preserva¬ tive. The timber absorbs so much liquid that it is full of the chemical preservative when it dries out again. You can also apply preservative by hand with a spray or a brush. This method is not very effective because penetration is poor. You should only use this method if there is little chance of attack by rot or insects. Figure 23.6 Students in a joinery workshop. Timber sizes Timber is usually sawn into standard size pieces with metric dimensions. For example, you should be able to obtain these joist sizes easily 50 x 100 mm 50 x 125 mm 50 x 150 mm Sawn timber is suitable for floor joists and roof pieces which do not require a high standard of finish. This timber looks and feels rough. Prepared timber Timber can also be prepared, if you need a smoother piece of wood for painting or polishing. You pre¬ pare timber by planing it square and smooth with a planing machine, which removes about 2 mm of timber from all the surfaces. After planing, a 50 x 100 mm piece of sawn timber is reduced to 46 x 96 mm. You must take the reduced dimensions into account when you draw up joinery details. Figure 23.6 shows you students preparing timber in the joinery workshop of a technical college. Timber technology Figure 23.7 Common joints used to fix two pieces of timber together: (a) butt joint; (b) dovetail joint; (c) finger joint; (d) grooved joint; (e) housing joint; (f) lapped joint; (g) mortice and tenon joint. 216 Building construction A carpenter usually works with sawn timber while a joiner works with planed timber. rectangular sections of timber at right angles. You see this joint in door frames which have dowels and wedges. CHECK YOUR UNDERSTANDING Joining timber Timber can be shaped to join pieces which lock together firmly. Besides cutting the pieces to fit, they are also usually glued. Sometimes small, round wooden dowels are used as pins. You can see from this list that joiners use a variety of joints to join two pieces of planed timber. Figure 23.7 shows you how the different joints look. 1. Butt joint A butt joint is not shaped and the two pieces are only joined by glue. These joints may have dowels inserted into them. 2. Dovetail joint A dovetail joint joins two pieces of timber at right angles. The shaped projection on one piece locks into a matching recess on the other piece. 3. Finger joint A finger joint is a machined joint that joins two pieces end to end so that the entire length is strong. 4. Grooved joint A grooved joint is used in tongue and grooved floors where a projection on the edge of one piece fits into a groove on the edge of the other piece. 5. Housing This joint joins two pieces that meet at right angles in the middle of their length. 6. Lapped joint A lapped joint is a simple interlocking joint, which can be half-lapped, rebated and notched. 7. Mortice and tenon This joint is the most popular joint for joining flat # Softwood trees are usually evergreen with need¬ les instead of leaves. # Softwood trees grow quickly. Hardwood trees have broad leaves and grow slowly. Softwood is easier to work than hardwood. It forms the bulk of the timber used in building construction. Seasoning is the gradual drying out of timber without causing defects. The moisture in timber should be about 20 per cent of its weight. # Trees are converted to timber by sawing. Timber should be treated with preservatives or painted to prevent attack by insects and fungus. Timber is cut to standard sizes in a sawmill. Planing reduces the size of cut timber by 2 mm all over. Joinery is the method for fitting pieces of planed timber together. REVISION EXERCISES AND QUESTIONS 1 2 3 4 Look at examples of hardwood and softwood timbers. What are the differences? What is the reason for seasoning timber? How do you apply preservative to timber? Draw the following types of joint: i) dovetail ii) mortice and tenon iii) lapped. Introduction Compression loading This chapter expands the information you need to know about the various stresses that affect the parts of a building. Two types of load create stresses: One of the main functions of the structure of a building is to transfer loads safely to the founda¬ tion and the soil. Solid walls are subjected to vertical compression loads, which is the reason for testing the compression strength of bricks, blocks and stones. You can see an example of compres¬ sion loading in Figure 24.1. 1. dead loads, which are created by the materials used to construct a building. Dead loads include walls, floors, roofs, finishes, services and fixed installations; 2. live or superimposed loads, which are created by the weights of the people and the movable fittings such as the furniture. Wind pressure is also a live load. Concrete is an excellent material under compression, which is why it is used in foundations. Figure 24.1 How the pressure at the base increases with the height of a wall. 217 218 Building construction Arches and lintels If you need to transfer a load sideways (bending stress), then you can construct an arch to carry the compression load down the sides until it becomes a vertical load at the bottom. An example of the compression forces at work in an arch is in Figure 24.2. Another method of transferring a load sideways is to bridge an opening with a lintel or beam. When the lintel or beam bends slightly under pressure this is called deflection. A beam is a horizontal member which transfers loads to the supports at each end. Examples of beams are floor joists, lintels, rafters or staircase strings. They are all able to bend slightly. The deflection (or bend) should not be more than l/360th of the span of the beam. Three types of stress cause a beam to bend slightly: 1. compression, which forces material in the top half of the beam together; 2. tension, which pulls the material in the bottom half of the beam apart; 3. shear, which bears down on the beam to force it to break. There is an example of a bending stress in Figure 24.3. Because concrete is not strong in tension, it is not suitable as a structural member in mass form. You need to stiffen it with reinforcement bars at the point of the tension stresses. You can control the shear forces in concrete by inserting vertical stirrups in the beam. Columns Columns and piers also help to spread compres¬ sion loads if they are constructed properly. A col¬ umn is a vertical structure that is not attached to walls. Columns transfer the loads from beams to the foundations. If the columns are too narrow for their height, then they will be unstable and bend or buckle which leads to collapse (Figure 24.4). Steel reinforcement in columns spreads the stresses so that the columns can be smaller. Slabs Reinforced concrete slabs which form floors and roofs are designed as a series of adjacent beams that span between wall or beam supports. Live and dead loads Additional load at the base of the arch Figure 24.2 Compression loads on an arch. Structural loads 219 Top of the beam shortens: the material Pressure from live and dead loads Figure 24.4 Loading columns. Types of loads Loads can be: ® uniformly distributed; # point loads. Uniformly distributed loads (UDL) transfer stresses evenly to a structural member. For ex¬ ample, a strip foundation that supports a loadbearing wall will transfer the forces along the length of the foundation because of the effect of the brick bonding. You can see an example of this process in Figure 24.5. Point loads transfer load stresses to a single structural member. An example of this is the end of a roof truss that rests on a wall or beam. Forces in a roof truss A roof truss has a triangular structure to make it stiff enough to bear the forces of the roof. Figure 220 Building construction No bending stress or shear supports the UDL of the wall Figure 24.5 Uniformly distributed loads on a strip foundation. Figure 24.6 The forces on a trussed rafter roof. 24.6 describes which parts of the structure respond to the loads. A strut is the compression member that runs between the rafter and the roof tie. The rafter tends to sag under the weight of the roof and pushes down on the strut, which takes the compression. The strut may take tension temporarily when the roof slope is lifted up by the wind on the down¬ wind side. A tie is the bottom horizontal member of a truss. It spans the extreme ends of a truss and pulls against the thrust of the rafters. A brace stiffens the roof truss when the wind force bears on the roof. It can be in tension or compression. Reactions and moments V Reactions occur at the ends of loaded structural members when the loads are transferred to the supporting construction. Moments are a measurement of a reaction. 221 Structural loads Measuring reactions Uniformly distributed Load (UDL) CHECK YOUR UNDERSTANDING V_V V V V K7 V X7^ JV\7\7yy\7U\7 L— UDL A Reaction 'A' Reaction 'B' A With a UDL the reactions at 'A' and 'B' are equal and are therefore each equal to half of the amount of the UDL. i.e. = reaction at 'A' or 'B' The building structures must support and resist the loads and forces acting upon them. Loads can be live loads or dead loads. Wind pressure also applies a load. Most loads are compressed, except in suspended structures which have tension forces. Tension is caused by suspended members bending under pressure. Downward pressures in suspended structures create shear forces. Loads are uniformly distributed or are point loads. Point loads C Jz. 7K Reaction 'A' Reaction 'B‘ With a central point load the reactions at 'A1 and 'B' are as for the UDL. y * I 5 REVISION EXERCISES AND QUESTIONS 2 3 load 7 Reaction 'A' 1 z 4 Reaction 'B' 5 When the point load is closer to one support the reaction at this support will be greater than at the one further away. To measure the reactions, moments are taken about one of the reactions. i.e. Moments about Reaction 'A' load x x = reaction B x (x + y) „ . „ load x x Reaction B = —-— (x + y) Example To find reactions A point load of 50 kN is 3 metres from Reaction A on a beam 10 metres long Moments about 'A' 50 X 3 = B x 10 Thus reaction B = ^ X ^ = 15 kN 10 aua reaction A = 50-15= 35 kN How does an arch differ from a beam when it spans an opening? Draw a beam with a UDL and show the reactions at the supports. What happens to a tall, narrow unreinforced column? Figure 24.6 shows a roof truss. Which forces act on the main parts? A beam is 9 5 metres long. It has a point load 3.25 metres from one end. If the load is 63 kN, then what are the moments at each end? Answers to revision exercises and questions Introduction This section provides you with all the answers to the variety of questions and exercises given in the book. Always try a question or exercise yourself before you look at the answer. This will increase your understanding of the topic and give you practice in answering questions. If you are not sure of a particular answer, re-read the relevant section or chapter in the book to revise the work. You need to understand why a question has a particular answer, so that you can apply your understanding to similar types of question or exercise in your examinations and course assignments. To revise a topic quickly you can also refer to the ‘Check your understanding’ sections given at the end of each chapter, and the list of key words with definitions given at the end of the book. Hints to answering questions in examinations and course work Read all the questions carefully before you try anything. Make sure that you understand what each question is asking you to do. Plan the time that you will spend on each question. Use the marks as a guide: the more marks a question is worth, the more time it is worth spending on it. If you have a choice of questions, try to make your choice and stick to it. Don’t change your mind halfway through the examination. Make sure that you earn all the ‘easy’ marks. Do not spend too long on a question you find difficult. Leave it; if you have time, you can try it again later when you have finished all the other questions. 222 □ I1 Keep an eye on the time. Make sure that you try all the questions you are required to an¬ swer. Always present your work as clearly as you can, whether you are writing or drawing. Make your work easy to follow for the examiner or assessor. Try and allow some time at the end to check your answers and improve them. In practical work, make sure that you under¬ stand what you are being asked to do by re¬ reading the question before you start. Follow all instructions carefully. Chapter 1 1 A building worker should have a hard hat, rubber boots and gloves. 2 You should inspect excavations after heavy rain to check that the sides are stable. 3 If someone receives a serious shock you should: turn off the electric current; make the person comfortable; • keep the person warm; check the pulse; apply artificial respiration; contact an ambulance or medical facility. 4 Three dangerous materials on a building site are: i) petrol; ii) explosives; iii) paraffin. You may be able to think of other dangerous materials. 5 A site is healthy if it has space for the workers to take rest breaks, cook food and for sanita¬ tion facilities. Answers to revision exercises and questions Chapter 2 1 The client needs finance and a site. 2 The structural engineer carries out the calcula¬ tions for the main parts of the structure. 3 The contractor uses a subcontractor’s special expertise to do parts of the construction work. 4 i) Planning controls are concerned with the environmental and design aspects of the work. ii) Building regulations are concerned with the structure of the building. 5 The contractor buys: i) paint from a builder’s merchant; ii) sand from a quarry; iii) timber from a timber merchant. 6 Look for building uses such as medical, ser¬ vices, schools, residential or commercial. How many more can you find in your area? 7 Put this information neatly on a map of your area. 3 A plan, a section and an elevation are the different views of a building that explain the relationship of the structure. 4 A specification is the description of how to do the building work. A bill of quantities is the estimate of the quantities of material required as a basis for pricing a job. 5 Window 6 Chapter 3 1 Any three out of these five factors can increase building costs: i) soil conditions; ii) ground water; iii) sloping ground; iv) availability of services; v) proximity to other buildings. 2 The three services that are useful for site devel¬ opment are: i) water; ii) electricity; iii) drainage. 223 Door Window i) 50m2 x 9 = *450 ii) 60m2 X 120 = *7 200 iii) 60m2 x 73 = *4 380 iv) 215m2 X 60 = *12 900 Total = *24 930 Chapter 5 1 The working drawings and specifications are the documents that enable the contractor and subcontractors to carry out their work. 2 Three main responsibilities of the main con¬ tractor are to: i) employ skilled workers; ii) complete a job on time; iii) observe health and safety requirements. You may want to add other answers to this question. 3 A contractor can lay a hardcore road base down at the start of the contract. You should be able to find a survey map in your local planning office. 4 Termite nests should be destroyed because termites will attack and destroy untreated timber. Chapter 4 1 A site plan positions the building on the site. 5 A contractor should dig trial holes before work begins to find out the condition of the ground and the level of the natural water table. 6 Your drawing should be similar to Figure 5.1. It should show access to the site and clear work¬ ing space around the areas under construction. 3 Manholes in the road indicate the presence of drains. 4 Use a 30 metre tape and a magnetic compass. Reduce your building to a 1:100 or 1:50 scale so that it fits on a sheet of paper. 5 2 The documents which you need to have ap¬ proved for building work to start are: i) the working drawings; ii) the specification. 224 Building construction Chapter 6 1 In a 3-A-5 triangle, 3 = 750 mm, 4 = 1000 mm, 5 = 1250 mm 3 The purpose of a raft foundation is to spread the load on poor soils. Raft foundations are also used if the load is small. 2 If the diagonals are not equal, then you should move the pegs until the corners are square. 4 3 Make sure that the length of the string forming the triangle adds up to a multiple of 12 so that you know that you have a 3-4-5 triangle. i) The width of a foundation depends on the load and bearing capacity of the soil, ii) The thickness of a strip foundation is meas¬ ured by a 45° angle from the base of the wall. 4 See Table 6.4 for an example. Make a trammel that is the same length as the fixed radius of the circle. 5 See Figure 8.1. 6 Strip foundation: Concrete = *650 Brickwork = *1000 Backfill = *200 Total = *1850 per metre run Deep strip foundation: Cost of concrete = *650 x 3 = *1950 per metre run 5 You set up a site datum mark by using a survey datum level or a convenient fixed object above ground level such as a manhole cover. You find the levels with a levelling instrument, a staff and a wooden peg as the datum. Chapter 7 1 See Figure 7.7 2 i) Cut and fill excavation uses excavated soil to build up the levels at the lower end. This reduces the total amount of excavation re¬ quired to produce a level site, ii) Stepped foundations reduce the amount of trench foundation required. Chapter 9 1 i) The main functions of load-bearing walls are to transfer loads to the foundations, support the weights of floors and roofs and resist wind pressure. ii) The main functions of non-load-bearing walls are to separate spaces, provide sound insulation and fire resistance. 2 See Figure 9-26. 3 Foundations are built below ground level to protect against impact and to reduce the effect of climatic variations. 3 You can use cement, sand, aggregates, laterite, fuel ash and timber shavings to make cementbased blocks in 1:6 or 1:8 mixtures. 4 You should remove topsoil because it is not firm enough to support building loads; it con¬ tains vegetation and is less compact. 4 A damp-proof course is a waterproof barrier to prevent the entry of moisture. 5 i) To clear a site you use a bulldozer. ii) To dig narrow trenches you use a backacter. iii) To remove soil from an excavation you use a mechanical shovel and tipper truck. A closer maintains the bond in the brickwork where openings or corners interrupt the course. 6 See Figure 9-17. 7 Set the profiles so that they are level. Then make a boning rod so that it reaches from the top of the profile to the bottom of the trench. Sight between profiles until the boning rod is aligned. You position the first bricks correctly by stretch¬ ing lines between profiles on outer wall sur¬ faces. You need to mark corners in wet mortar. 8 The advantages of cavity wall construction are that in cold, wet conditions it keeps the build¬ ing interior warmer and drier. Cavity walls can also insulate against heat gain. 5 6 Chapter 8 1 1250 kg x 10/1000 = 12.5 kN approximately Chapter 10 1 See Figure 10.2 and Table 10.1. 2 2 31 250 kg = 312.5 kN Area of foundation = 312.5 + 52 = 6 m2 Length of side of foundation = V~6 m2 = 2.45 m (say 2500 mm) i) A throat increases the rate of flow of the hot gases and improves combustion, ii) A gathering links the top of the fireplace to the narrower mouth of the flue. Answers to revision exercises and questions 3 50 mm. 4 See Figure 10.4. Chapter 11 1 An oversite concrete slab can be used as: i) a finished floor slab; ii) a slab beneath a suspended timber floor; iii) a raft foundation. 2 A honeycomb sleeper wall supports timber floor joists and allows the air to circulate. 3 See Figure 11.4. 4 A wet concrete slab is covered with polythene sheets for seven days. It should be kept moist so that the moisture evaporates slowly. It can also be covered with hessian, which is lightly watered at intervals and removed after seven days. You use a tamp to compact and level the surface. 5 6 Steel reinforcement introduces tension in the bottom of the slab to counteract the poor strength of concrete when under tension or compression. 2 5 Roof trusses support purlins, which support rafters. Trussed rafters use all rafters as trusses without purlins. 6 See Figure 12.18. 7 You lay bituminous felt in layers. The first layer should be nailed to the boarding. The end of the second layer should overlap the first layer. You then apply a layer of bitumen adhesive before adding a final coat of bitumen. You finish by sprinkling white stone chippings on the bitument to provide protection and to re¬ flect heat. Chapter 13 1 A scaffold is stable if it has: i) a firm and level base; ii) diagonal bracing; iii) level platforms; iv) ties to the building under construction. 2 The four poles used in a putlog scaffold are: i) standard, which is a vertical pole that transfers loads to the ground; ii) ledger, which is a horizontal pole that ties the standards together; iii) putlogs, which are horizontal poles sup¬ porting the platform; iv) braces, which are diagonal poles that stiffen the scaffolding. 3 See Figure 13-1. 4 See Figure 13.2. 5 The triangular shapes of the diagonal braces stiffen the scaffolding. 6 A comparison of the advantages and disadvan¬ tages of timber and metal scaffolding. See Figure 11.7. Chapter 12 1 The function of a roof is to: i) keep out wind and rain; ii) weigh down the structure of the house; iii) keep the interior cool. You may have other answers to this question. i) Pitch is the slope of the roof from a hori¬ zontal level. ii) A hip is the intersection of two external roof slopes. iii) A gang nail plate is the metal plate that joins the beams in a trussed rafter. iv) A gauge is the space between tiling bat¬ tens. v) A parapet wall is a projection above the level of the roof. 3 A flat roof needs some slope to drain rain water. A minimum pitch is 1:80. 4 i) The structural members support the frame¬ work of the roof, ii) The main members are the: # rafters; # joists; # purlins; # trussed rafters. 225 Timber scaffolding Advantages Disadvantages i) cheap; i) slower to put up; ii) materials available; ii) joints are not as reliable; iii) no special fittings iii) hard to detect required. defects in the timber. Metal scaffolding Advantages i) durable; ii) more adaptable; iii) consistent quality. Disadvantages i) more expensive; ii) more fittings; iii) must be stored and protected. 226 Building construction Chapter 14 1 The formula is 225 mm + 2 risers = 700 mm 2 risers = 700 - 225 mm = 475 mm 1 riser = 237.5 mm 2 See Figure 14.8. 3 See Figure 14.5. 4 See Figure 14.6. 5 See Figure 14.2. Chapter 17 1 If drains are too steep, then solid matter is left behind because water flows through too quickly. If the drains are too shallow, then the water does not flow strongly enough to carry the solid matter away. 2 The fall in the drain is 45 000/40 = 1125 mm Depth of invert at lower end is 1125 + 875 mm = 2000 mm 3 Concrete, clay and iron are rigid materials. Plastic and pitchfibre are flexible materials. 4 i) Hydraulic test; ii) Ball test; iii) Mirror and torch test. 5 See Figure 17.5. 6 A septic tank treats the solid effluent by break¬ ing it down under bacterial action. A cesspool does not break effluent down and must be emptied regularly. 7 You use a boning rod to check the depth of the drain run so that it falls to the correct depth. 8 i) The purpose of a manhole is to: a) give access for cleaning and inspection; b) allow for changes in direction of the drain run; c) allow connecting drains to join the main drain. ii) The reason for venting a drainage system is to prevent the build up of gas pressure in the drains. iii) Branch drains connect to the main drain at a manhole and in the direction of the flow. 9 The waste from a WC flows directly to a man¬ hole. Sink waste goes through a gully. Chapter 15 1 2 i) Putty; ii) Beads. 3 See Figure 15.4. 4 i) Rim-fixed; ii) Morticed. 5 See Figure 15.1. Chapter 16 1 For a side-hung window you need a pair of hinges, a casement handle and catch and a casement stay and pins. 2 The window should be 1190 x 1490 mm to allow 10 mm all around for bedding. 3 You should point joints with mastic and put drip mouldings and grooves in the rails. 4 The purpose of a cill is to push rainwater flowing down a window surface clear of the brickwork underneath. 5 The three ways that metal windows are better than timber are: i) the smaller sections allow in more daylight; ii) the windows do not rot and are resistant to termites; iii) the windows are simple to make. Chapter 18 1 Rivers, wells and reservoirs. 2 A water treatment plant removes bacteria and filters out other matter. 3 i) Stored water is best for washing and cleaning. ii) Mains water is best for drinking and cook¬ ing. 4 i) A stopcock shuts off the water supply. ii) A ball valve controls the amount of water supplied to a tank or cistern. 5 0 An active solar water heating system needs a pump to circulate the water. A passive Answers to revision exercises and questions system circulates the water naturally due to a thermo-syphon action, ii) The main advantages of the active system are that: • it can be placed up high to reach more sunlight; • it is easier to protect from damage. The main disadvantages of the active system are that: • it needs a pump and an electrical supply; • it can be more difficult to maintain. The main advantages of the passive system are that: • it requires fewer parts; • it is easier to maintain. The main disadvantages axe that: • it does not receive as much sunlight; • it can be damaged more easily. 6. 2 3 • applying a skim coat of neat plaster. 4 You prepare a wall for a coat of plaster by: • applying plaster daubs at spaced intervals; • level the daubs horizontally and vertically; • apply the plaster in vertical bands over the daubs; • apply a backing coat of plaster in between the screeds and level off with a screeding board. 5 To prepare timber you follow these steps: • rub down; • dust; • seal knots; • prime; • apply filler; • rub down; • apply undercoat; • rub down; • apply gloss coat. 6 You put a bonded screed on a concrete floor by placing timber battens with daubs of ce¬ ment about a metre apart. You fill in the gaps with the screed mix and level them with a screed board. Compression and capillary joints. Chapter 19 1 The standard colour codes are: • brown = live; • blue = neutral; • yellow/green = earth. Earthing allows an electrical current to flow into the ground if a fault occurs which allows a live wire to come into contact with equip¬ ment. The earthing forces the fuse to blow, which shuts off the supply and prevents the consumer from receiving a shock. Chapter 21 1 The purpose of water in a concrete mix is to hydrate the cement and make it workable. 2 When you store cement you should: • check the date of manufacture; • store it off the ground; • protect it from rain; • limit the height of the stacks; • use older cement first. 3 To test for silt you should mix sand and water in a measuring beaker. Then measure the amount of silt that settles to the bottom. There should be less than 5 per cent of the total volume. 4 i) Graded aggregate is aggregate with a range of particle sizes. ii) Bulking of sand occurs when the moisture content of sand increases the total volume. iii) Slump is the measurable level of collapse of a sample of concrete. A slump test checks the amount of water content in the con¬ crete. 5 Two boxes of cement = Four boxes of sand Eight boxes of aggregate W= Vx I 2000 = 240 x / I = 2000/240 = 8.3 amps 4 See Figure 19.2. Chapter 20 1 You should plaster walls and ceilings to make a smooth finish to provide a base for decora¬ tion. 2 i) Key means the adhesion created by the roughness of a surface, ii) Suction means the penetration of the mix¬ ture into the surface of the backing. 3 You fix plasterboard to a ceiling by: • nailing; • filling nail holes; • filling and scrimming joints; 227 50 kg = 0.035 m3 = 0.070 m3 = 0.140 m3 228 Building construction = 30 litres = 0.030 m3 4 5 Chapter 23 1 The main differences between hardwood and = 0.275 m3 softwood are: Volume of concrete produced # hardwood has closer grain lines; per batch = 0.275 x 2/3 = 0.18 m3 # hardwood is harder to cut or plane; # hardwood is darker; To produce 3 m3 of concrete you need # hardwood is more dense; 3.00/0.018 m3 = 16.6 (say 17 bags) of cement # hardwood resists indentation more. Material needed: Cement = 17 bags = 850 kg 2 The reason for seasoning timber is to reduce Sand = 0.07 x 17 = 1.19 m3 the amount of moisture in the wood to an Aggregates = 0.14 x 17 = 2.38 m3 equilibrium with the moisture in the atmos¬ Water =30x17 =510 litres phere. You can check the moisture content of sand by 3 You apply preservative to timber by: weighing it in its natural state, heating it until it # pressure impregnation; is completely dry and then weighing it again. # steeping; # painting. Water Total bulk volume 6 Chapter 22 1 Non-cohesive particles such as sand separate. Cohesive particles such as clay stick together. 2 3 A natural foundation supports: # superimposed loads made up of the occu¬ pants, furniture, fittings and plant; # dead loads made up of the structure of the building. These types of soil are poor for building on: # made-up ground; # black cotton; # some types of clay. 4 You should dig trial holes to check the condi¬ tion of the soil and to help design the correct foundations. 5 If the area = 118/48 kN = 2.46 m2, then the si of the base is V2.46 = 1568 X 1568 mm 4 See Figure 23.6. Chapter 24 1 An arch transfers a load vertically under com¬ pression at the top. A beam transfers a load horizontally under compression at the bottom. 2 See Figure 24.3. 3 If a column is too high, then it will buckle or bend under stress. A tall column requires rein¬ forcement. 4 See Figure 24.6. i) The struts take compression forces. The ties take tension forces. The braces take tension or compression forces. 5 i) The reaction at A = 41.5 kN ii) The reaction at B = 21.5 kN Abutment a) The point where an arch meets a wall. b) A junction, such as the point where the edges join on a parapet roof. Adhesion Strong, firm contact between surfaces. Aggregates The stones and gravel used to make con¬ crete. Air brick A ventilator that fits into the brickwork to ventilate suspended timber ground floors. Amperage The unit of electrical current. Arch A structure of wedge-shaped stones or pieces that support each other by mutual pressure and curve up¬ wards. Architrave A wooden facing strip fixed around a door frame or lining to cover the joint between the plaster and the frame. Arris The corner where two surfaces meet. Artificial foundation The structure that lies between the building and the natural foundation. Asphalt A dark, hard substance mixed with rock chips or other materials and used for paving or roofing. Auger A spiral-shaped cutter used to remove a cylinder of soil. Back The vertical brick surface that makes the opening for the fireplace. Baluster The infill between the handrail and the string on a staircase. Balustrade The protection erected on the outer edge of a staircase. Barge board A board that hides and protects the gable end of a roof. Batten A piece of timber which is fixed in place to attach another part of the structure to. Beam A large straight piece of timber or metal that forms one of the main staictural members of a building. Bedding To lay in layers or on a surface. Bevel A sloping edge to a board or piece of timber. Bituminous felt A roof-covering material that is treated with a mineral substance. Blinding A smooth level finish on hardcore. Boiler An apparatus for heating water. Bonding a) The overlapping connection of one stone or brick with another. b) Earthing in electrical circuits. Boning rod A T-shaped timber rod used for taking levels. Brace A piece of timber that stiffens a larger structure. Breast The brickwork for a fireplace that projects into a room. Builder’s square A frame with a right-angled corner. Butt A joint formed between the squared ends of two jointed pieces that do not overlap. Carriage The support underneath a staircase. Casement A side-hung opening window. Caulk The filler in a spigot or socket joint of a drain pipe that makes the seal watertight. Cavity walls Two layers of wall with a space in between. Cement a) The process of bonding two surfaces together. b) A combination of limestone and silica used in making concrete. Centring A timber piece with the same shape as an arch that is used to achieve the upward curve of an arch under construction. Cesspool A pit or pool for collecting waste water. Chase The groove cut in a wall to take conduits or cables. Chimney The brick structure that carries the flue above a roof. Cill A horizontal member at the base of a door or win¬ dow. Cladding One material that covers another. Closer A brick cut in half along its length. Compression The volume of a material being reduced under pressure. Concrete A mixture of materials, such as cement, sand, gravel and water, that bond into a stronger mass. Consumer unit Distribution unit for electricity in a build¬ ing. Contours Lines that show the amount and direction of slope. Corbel The projection of brickwork from a wall. Course A complete layer of bricks including the mortar. Cramp A metal fastening. Crazing A covering of fine surface cracks on plaster. Datum level The baseline for survey levels. Datum level mark A mark on survey maps to indicate the height above sea level. Dead loads These are the weights of the fixed parts of buildings such as the walls, floors, roofs and fittings. Deflection When a level beam or surface bends down¬ ward from a horizontal line. 229 230 Building construction Density The proportion of a mass to bulk or volume. Dowel A wooden pin that secures timber joints. Down service The water supply from the cold water tank. Dpc A layer of moisture-proof material laid on brickwork to prevent rising damp in walls. Dpm A layer of moisture-proof material laid under a concrete slab and screed to prevent rising damp in floors. Drain A pipe to carry waste water or rainwater away from a building. Dressing Cutting stones into suitable shapes and sizes for building work. Dry lining A method of finishing walls with plasterboard instead of plaster. Eaves The bottom edges of pitched roofs. Effluent The outflow from a sewage treatment plant. Elevations External views of a building that show the general appearance. Excavation The process of digging out the ground on a site. Face The exposed surface of a brick or block. Fascia The vertical timber board fitted to the roof joists to secure the gutters. Fillet A narrow piece of wood or metal. Fillet weld A material laid down in the angle of the intersection between two surfaces. Fire resistance The ability of a material to resist fire for a specified period of time. Firring Tapered strip of wood that forms a slope on flat roofs. Flashing The metal covering for upright structures on a roof. Flight A series of steps between floors or a floor and landing. Flue a) The opening inside a chimney that takes the hot air, smoke or flames outside. b) A separate pipe that links to the chimney from a selfcontained appliance such as a boiler. Frame A solid timber or metal structure fixed to a wall. Gable The triangular portion of wall between the sloping edges of a pitched roof. Gaskin The yarn used to seal spaces in pipe joints. Gauge a) Width of a row of slates. b) A standard of measurement. Gloss paint Paint containing varnish to give it a hard, shiny finish. Going The horizontal distance between risers. Gusset Piece of plywood that joins timber trusses. Hardcore Broken brick or stone used as a base for ground-floor concrete slabs. Haunch A sloping mortar fillet for bedding materials such as tiles. Header A brick laid in a wall so that the smallest surface is visible. Hearth The fireproof horizontal base of a fireplace. Hinge The joint on which a door turns. Honeycomb sleeper walls Brick or block walls built over oversite concrete so that air can circulate underneath. Hopper a) A fitting at the head of a rainwater pipe attached to a flat roof. b) The container for weighing and loading materials to go in a concrete mixer. Hydrate A compound that can expel and absorb water. Immersion heater An electrical apparatus in the water in a boiler, used for heating water. In situ Constructing something, such as lintel, in position. Inspection chamber A manhole that gives access to a drain run. Insulation The material used to reduce energy loss in walls and roofs. Invert The depth from the datum level to the lowest part of a drain. Ironmongery Metal hardware fitted to doors and win¬ dows. Jamb The sidepiece or post of a door or fireplace. Joint The point where two surfaces or pieces meet. Joist A steel or timber beam that supports a floor or roof. Landing The level space that breaks up a flight of stairs. Latch A door catch lifted by a lever. Laterite A clay formed by weathering, which is com¬ posed mainly of iron and aluminium hydroxides. Lining A timber framework inserted into an opening in an internal wall. Lintel A beam that spans an opening to support the load of the wall above. Live loads The weights of the people, furniture and machines in a building. Load-bearing wall It carries the weight of a structure such as a roof or floor above it. Louvres Individual pieces of glass held in position in a window by metal clips. Manhole The access point to the drainage system. Masonry Building work in stone, bricks or blocks. Mastic An oily cement. Member A piece, which is usually timber or metal, that forms part of an entire structure. Mortar A mixture of cement and sand used in brick and blockwork. Mortice A hole in a timber frame that takes another piece of timber or a fitting. Moulding A shaped piece of timber. Natural foundation The ground underneath the base of the building after excavation. Noggin A piece of wood inserted in a wall to receive nails. Non-load-bearing wall It does not carry the weight of a structure above it. Nosing The part of the tread that projects beyond the riser. Key words 231 Ohm The unit of electrical resistance. Opening light The opening portion of a window. Scale The measure for drawing objects to a smaller size while keeping the correct proportions. Screed Parapet A brickwork projection above the edge of a roof. Partition A wall that separates two rooms. Percolation test A test to see how long it takes for water to filter into the soil. Perpend a) The vertical joint running through brickwork. b) A stone running through a wall from face to face. Pier a) A free-standing column of brickwork. b) A projection from the surface of a wall which stiffens it. Piles These are load-bearing cylinders driven into the ground to support a foundation. Pit A hole that is excavated in the ground for founda¬ tions. Pitch The slope of a roof or the angle of the nosings on a staircase. Plant The mechanical equipment used on a building site. Plate The timber piece used at the bottom of structures to spread a load. Plumb-bob A weight at the end of a line to show vertical levels. Plumb-line A vertical line. Pneumatic drill A drill that is driven by compressed air. Polings These are vertical timber boards that support the soil in a trench. Precasting Making something, such as a lintel before putting it in position. Profile A timber board that marks the boundaries of excavations and walls. Purlin A beam that supports the rafters or roof sheeting. Putlog Cross-pieces of a scaffold that have one end built into a building. a) A band of plaster laid on the surface of a wall as a guide to the thickness of the coat. b) A layer of mortar finishing off the surface of a floor to make it level for fixing other finishes. Sections Show the depth of the foundations, the levels of the floors and roofs and other construction details. Septic tank A tank in which oxygen is removed and sewage is broken down by anaerobic bacteria. Sewer The main drain for moving water-borne human waste. Shear A force on a beam. Site datum A fixed point, such as a wooden peg, used to measure the different levels of a building. Slab A large area of thin concrete. Soakaway An area where water percolates into the soil. Socket Outlet for the electrical wiring which takes plugs. Soffit The horizontal underside of a surface. Span The horizontal distance between the supports of structural members. Specification Document that describes the standards of workmanship and materials required for a building project. Spigot The end of a pipe that goes into a socket. Spirit level A glass tube that shows a central bubble when a surface is level. Stile An outer vertical piece of a door frame. Stopcock A short pipe opened and stopped by turning a handle or a key. Stretcher A brick or block placed so that its length is the same direction as a wall. String The beam which supports the treads and risers in a staircase. Strut A structural beam under compression. Stud partition A timber partition. Subsoil The soil below ground level after excavation of the topsoil Substructure The part of the building below ground level. Suction The process of absorbing water in a mixture. Surface water The rainwater that falls on the hard sur¬ faces around a building. Quoin The external corner where two wall surfaces meet. Racking back The stepping back of brickwork to reduce the height of a wall. Raft foundation A reinforced concrete slab used in ground with poor bearing capacity. Rafter An inclined beam that supports a roof. Rebate A groove cut in one board to hold the end of another board. Reinforced concrete Concrete strengthened by embed¬ ded steel bars or mesh. Render A cement and sand plaster applied to the exter¬ nal surfaces of a building. Reveal The side surface of a door or window opening. Ridge A timber at the apex of a roof that takes the tops of the rafters. Ring main The electrical circuit that connects the socket outlets in a building. Riser The vertical surface of a step. Rising main The pipework for the water supply in a building. Sash The entire moving part of a window, including the frame and glass. Trammel A board used to make a circle. Transom Cross-piece on a scaffold, a window or a door. Tread The horizontal surface of a step. Trial holes Holes dug in the ground as part of site investigation. Truss A framed structure for supporting a weight. Truss-beam a) A wooden beam strengthened by a steel tie-rod. b) A steel framework acting as a beam. Undercoat A coat of paint put on before the finishing coat. UPVC A plastic material used for making pipes, door and window frames. 232 Building construction Vent A pipe that releases pressure from a drainage sys¬ tem or hot water installation. Ventilation The method of circulating fresh air into a room. Verge The edge of a roof that projects beyond a gable. Vitrified clay Clay fired at a very high temperature to make it waterproof. Voltage The pressure of the electric current. Walings These are horizontal timber boards that support polings. Wall plate The piece used as a base for fixing floor joists. Wall tie A fitting used to tie the inner and outer surfaces of a cavity wall. Water table The natural level of water in the ground. Wattage The unit of electrical power. Wind loads These are the pressures on the walls and roofs from the wind. Index (Page numbers in bold refer to illustrations) abutment 63, 229 access gates: for construction site 18 access road: temporary, to site 20 acrylic primers 188 African house: roof of 92 aggregates: for concrete 197, 198, 229 grading 201-2 weight of 200 agricultural buildings 8 air bricks 84, 229 aluminium sheets: for roofs 93 aluminium wood primer 188 amperage 179 apprentices 6 arches 6l-4 centring 63 compression loading on 218 making brick 63 parts of 62-3 segmental 62 semicircular 62 stages in building 64 types of 63 architect 5 drawing office 5 architrave 229 arris 52, 229 asphalt: mastic 110, 113 for roofs 93 auger 33, 45, 229 mechanical 33, 36, 37 back: of fireplace 76 backacter: use of 31, 33, 36, 37 ball drain test 151, 152 ball valve 168, 171 baluster 119 inclined 126 section of 127 steel 127 vertical 126 balustrades 119, 121 barge board 229 base boards: for scaffolding 115 base plates: for scaffolding 115 basements: excavating 30 on sloping site 34 basin 161 bat: brick 52 bath 161 beams 61 compression load on 218 and steel anchors 62 bed: brick 52 bed joint 52 bending stress 218 in a beam 219 bevel 229 bill of quantities 6, 13, 16 sample page 16 binders 97 paint 188 bituminous felt: laying 110 for roofs 93, 109 blinding: for floors 82, 83, 229 blockboard 85, 88 blocks: bonding 72, 73 cement-based 49, 50 choice of 69 concrete 50 concrete partition walls 70, 71, 72-3 curing 69 hollow 50, 69 landcrete 50 manufacture 69 in situ 69 materials for 69 piers 85 plastering 183 safety with 3, 7 sandcrete 50 solid 50, 69 standard dimensions 50, 51 for walls 68-70 weights 69 boilers, hot water 171-2 bolts, door 136 security 135 bonding: altering 54 block 72, 73 in blockwork 54-5 in brickwork 53-5, 229 stones 66 in stonework 54 bond patterns: for tiles 102 boning rod 31, 229 use of 32, 33 bottom-hung windows 139 boundaries: site 18 braces: door 130-1 roof 220 for scaffolding 115, 229 breast: of fireplace 76 brick gauge 52 bricklaying: materials 55 technical words for 52 tools and equipment 55 bricks 7 arches 63 for external walls 49, 50 building 55-8 openings in 58-65 piers 85 plastering 183 safety with 3 standard dimensions 50, 51 bridles: for scaffolding 115 builders’ merchants 7 building: circular 27 setting out 23-9 square or rectangular 23-7 building control approval 13 building industry regulators 7 building inspector 7 building line 12 building materials: for external walls 49-52 suppliers 5, 7 building sites: clearing 18-22 cooking facilities 3 health and safety on 1^4 building surveyor: see surveyor building types: categories of 8 built-up roofing: see bituminous felt bulking: in sand 201 bulldozer 36, 37 burglar bars: on windows 145 butt 229 joint 215, 216 calcium plumbate primer 188 cardboard lattice: in doors 132, 133 carpenter 216 carpet: tiles 195 on timber floors 195 casement: fasteners 139 stays 139 window 139 cast iron pipes 149 caulk 229 caustic cleaners: storage of 2 cavity walls 65 construction 65 moisture entry prevention 66 cedar: softwood 211 cellulose thinners: storage of 2 cement 197 based, on concrete subfloor 190 233 234 precautions with 197 weight of 200 wet, on concrete subfloor 190 working with 3 centre: of arch 63 cesspool 147, 165 chase 229 chimney 76, 78 and window position 78 chipboard 85, 88 cill: door 130 masonry joint 143 see also window cill cistern l6l clay soil 208 clerk of works 6 client: for building 5 closed couple roof 95, 96 closer 52 in bonded blockwork 68 collar roof 95, 96 columns: compression loading on 218, 219 construction 58 digging pits for 30 pad foundations for 44, 209 setting out 26 commercial buildings 8 compression loading 217-18 on arch 218 concrete: compacting 202 compression loading 217 compression test 203 curing 84, 202, 203 drain pipes 149 for floors 81—4 casting 89 compression loading on 218 construction 88-90 curing 84 mix for 90 upper structure 86 for foundations 41 minimum mix for 42 lintels 59, 60, 6l making by volume 199-200 making by weight 200 materials for making 197-8 mixes 198-9 mixing by hand 204 moving 202 plastering 183-4 principles of deflection 88 reinforced roofs 107-9 reinforced staircases 120, 121 assembling 124, 125, 127 reinforcement in 204 slump test 203 technology 197-206 testing 203 Index see also strip foundations: concrete concrete mixer: position, on site 20, 200, 201, 204 construction documents 13-17 construction team 6 consumer units: of electricity 177 for hot water heater 178 for switch meter 178 contract supervisor 6 contractor’s team 5, 6-7 contours: site 12 cooker, electric: control unit 178 wiring 180 copings: brick-on-edge 109 on parapet roof 109 copper pipes 174-5 corbel 229 core: of door 133 corners, of building: setting out 24 corrugated iron sheets: for external walls 70 corrugated metal sheets: fixing 25 for roofs 93, 105, 106 corrugated mineral fibre: for roofs 93, 105, 106 costs: of developing site 9 couple roof 95, 96 closed 95, 96 course, brick 52 covering: of roofs 93, 95 crawl boards: on roofs 3, 106 crown: of arch 63 curing concrete 84, 202, 203 damp-proof course (dpc) 56, 57, 84, 229 vertical 65 damp-proof membrane (dpm) 34, 56, 229 for floors 82, 83 dangerous materials: storage of 2 using 2 datum level 12 dead loads: see load: dead deep strip foundations: see under strip foundations deflection: under pressure 218 depth: of arch 63 see also foundations: depth of design drawings 5 design specification 16 design team 5 detonators: record of 2 storage of 2 diesel: storage of 2 distribution bars 89 dog leg: on stairs 122 domestic buildings 8 doors 129-37 construction 130-3 dimensions 135 durability 129 framed, braced and battened 131, 133 frames and linings 137 flush 132, 133 ironmongery 134, 135, 136 ledged, braced and battened 131 operation 129 panelled 133 parts of 129-30 performance standards 129 dovetail joint 215, 216 dowel 229 down service: water 168 drainage 147-67 above ground 157-61 below ground 147-57 connections 158 location, on site 12 soil drainage 147-9 drains 147-53, 230 bedding 151, 152 calculating depth of 149, 152 clearing 152-3 excavating layout 150-1 laying near buildings 151 positions 151 testing 151-3 see also drainage; pipes dressing: stones 66 dry lining walls 184, 229 dump truck 36, 37 earthing: electricity 177 eaves 93, 102, 103, 229 effluent 147, 229 discharging 156-7 electric: boilers 171 geysers 171-2 meters 177 shocks 2 first aid for 2 electric current 177 alternating 179 direct 179 flow, and resistance 179 electrical: energy, components of 179 installations 177-82 domestic 178 theory 177-9 wiring 179-81 identification 179 electricity 2, 177 elevations 13, 14 emulsion paints 188 English bond 53, 54, 56 equipment: correct use of 1 for site clearance 20-1 see also mechanical equipment estimator 2 excavations 30-8 barriers round 1 cut and fill 34 depth of 33 heavy loads near 1 inspection of 1, 4 methods of 21 plant for 36, 37 supports in 1, 21, 30, 34, 35, 37 water in 30, 35, 37 working in 1 expanded polystyrene boards 113 explosives: record book for 2 storage of 2 external rendering 187 cracking 187 crazing 187 defects in 187 loss of adhesion 187 pebbledash 187 roughcast 187 scraped 187 smooth 187 Tyrolean 187 external walls: building materials for 49-52 characteristics 49 load-bearing 48 non-load bearing 48, 70 extrados 63 fall: of roof 93 fascia 93, 229 fibreboard, insulating: for roofs 113 fibre cement: fixing 106 rainwater pipes 164 for roofs 93, 105 fibreglass mats: for roofs 113 finger joint 215, 216 finishes: wall and floor 183-96 fireback 76, 79 fireplaces 76-9 building 78-9 dimensions 77 finishing off 79 parts of 76, 77 ^ working of 76 fire resistant doors 129 firrings 106 pieces, calculating dimensions for 107 Index first aid: box 3 contents 3 for electric shocks 2 flashing 229 flat roofs 93, 106-13 insulating 113 junctions on 110, 111 reinforced concrete 107-9 timber 106, 107 ventilation 112 wind effects on 113 Flemish bond 53, 55, 56 flight: of stairs 119 straight 121, 122 float: in water storage tank 168 floor: boarding 84 finishes 189-95 characteristics required 189-90 subfloors 190-5 floor joists 84 floor plans: house 13 floors 80-91 concrete ground-floor slabs 81 functions of 80 ground 80-1 construction 81-5 ground-floor slab 81 oversite concrete slab 80, 81, 83 laying, into bays 83 raft construction 81 upper 81 construction 85-91 flues 76-9 building 78-9 concrete cover 78 dimensions 77 offset, construction of 78 flush: doors 132, 133 mortar joint 52 panel 133 foreman, general 6 formwork: for columns 58 for concrete upper floors 89 erecting 2 for reinforced concrete stairs 124, 135, 127 foundations 39^17 artificial 39, 40, 41, 207 checks for correct 41 choice of 41 conditions affecting 39 depth of 30, 31, 42 as site datum level 27 excavation of 30, 37 in rock 34 loading 39, 40 natural 39, 40, 41, 207 plans 14, 15 and soil type 207-9 passim types of 41-6 width 42 see also stepped; strip frame: door 130, 131, 137 fixing 137 fuses 177, 180 values of 177 gable roof 94, 95, 229 galvanised iron: for roofs 93 galvanised joist hangers 85 galvanised steel ties: for roofs 113 gang nail plates 98 . gas boilers 172 gaskin 229 gathering: of fireplace 76 general foreman 6 glass, window 141, 143 clear 141 fixing 141, 143 obscure 141 safety 141 toughened 143 wired 143 gloves 38 for cement working 3 with bricks and blocks 3 gloss paint 188 on woodwork 188-9 goggles: use of 38 going: dimensions 122 for stairs 119 gravel soil 208 grooved joint 215, 216 grouting: between wall tiles 196 guard rails: for scaffolding 115 gully 147 surface water 166 gutter 111 box 163 bracket connection 163 dimensions 164 on flat roofs 163, 165 half-round 163 parapet 165 valley 163, 166 gypsum (plaster of Paris) 183, 184 half-round mortar joint 52 handles, door 135 lever 136 pull 136 handrails 119 for concrete stairs 127 height of 127 hardcore 229 bed, for floors 82, 83 depth under, as site datum level 27 height of, as site datum level 27 use of 31 hard hats 1, 38 notices about 4 hardwood 210-11 haunch: of arch 63, 229 hawk: for plastering 184 head: door 130 of fireplace 76 in timber partition 73 of water 174 of window 139, 143 header 229 bond 53 stones 66 health and safety: on building sites 1-4 heartwood: of tree 211 hearth 77 hinges, door 134, 135 butt 134, 135 strap 134, 135 window 139 hip roof 93, 95, 102, 105 holes: barriers for 3 hollow pot: floor 88 construction 90-1 structure 90 roof 108 honeycomb sleeper walls 84 housed joint 87 housing joint 215, 216 hydraulic drain test 151 hygiene: on building sites 3 immersion heaters 171, 174 independent scaffold 116 structure of 116 industrial buildings 8 insect screens: for windows 145 inspection chamber 147 insulation, for flat roofs: low density materials 113 reflective finishes 113 insulation jackets: for hot water cylinders 171 intermediate rails 133 internal walls: characteristics of 49 concrete block partitions 70, 71, 72-3 load-bearing 48, 49 non-load-bearing 49, 70-4 timber partitions 70, 71, 73-4 intrados: of arch 63 invert levels 229 calculating 149 ironmongery 229 door 134 for opening sash window 139 235 jack rafter 93 jambs: door 130 of fireplaces 77 and stile joint 143 window 139, 143 joiner 216 joints 149-50, 229 capillary, for copper pipes 175 compression, for copper pipes 175 for timber 215, 216 for uPVC 159, 160 between wall tiles 196 joists 229 ceiling 97 dimensions 85 for flat roofs 106 sizes 107 floor 84-5 trimmed 87 trimmer 87 trimming 87 keystone: of arch 63 labourers 6 ladders: regulations for 118 land: as building site 9 landing, stair 119, 121 half-space 122 quarter-space 122 lapped joint 215, 216 latches, door: cylinder night latch 134 fixing 135 lock and latch unit 134 spring-operated 134 lean-to roof 94, 95 ledgers: door 130-1 for scaffolding 112 levelling instrument 31, 32 levels: reducing 30, 31, 37 see also vertical levels light, window: fixed 139 opening 139, 140 lighting circuit 181 lime putty 184 limewashes 188 lining: door 130, 137 fixing 137 lintels 59-61, 68, 229 building 59 casting concrete 59 casting in situ 6l compression loading on 218 for fireplaces 79 forming 60 heights of 28 precasting concrete 6l standard dimensions 59 weights of 59 lipping: of panel door 133 236 live loads: see load: live load-bearing capacity: of floors 28 of rafters 28 of roof trusses 28 of soil 207 of wall plates 28 loads: dead 39, 207, 217 live (superimposed) 39, 207, 217 structural 217-21 types of 219 wind 39, 207, 217 see also compression loading lock block: for doors 133 locks, door: dead lock 134 fixing 135 lock and latch unit 134 morticed 135 recessed 136 rim 136 louvre windows 139, 141 main contractor 6, 13 responsibilities 18 mains water: pipes 168 rising 168 manhole 147, 149 building 153, 154 dimensions 153 mask: with cement use 3 when excavating 1 masonry 48 blocks 68 dimensions 50, 51 materials 50 mastic asphalt: see under asphalt mechanical equipment: for excavations 31, 36, 37 mechanical shovel 36, 37 medullary rays: of tree 211 mesh reinforcement 43 metal: painting 188, 189 rainwater pipes 164 metal hanger 87 metal ties: with concrete partition walls 72 metal windows 143, 145 parts of 144 on precast concrete cill 145 mirror and torch drain test 151, 152 moments 220 mono-pitch roof 94, 95 mortar 50, 52, 229 types of joints 52 mortice and tenon joint 215, 216 mullion window 139 muntins 133 Index nailing: secret 85 natural features: on site 12 newel, stair 119 newel post 119, 124 noggins 73^ nosing, stair 119 ohm 179 oil fired boilers 172 ‘O’ ring 159, 160 ordnance datum level mark 10 overhanging roof 108 oversite concrete slab: height as site datum level 27 see also under floors pad foundation 42, 44 bearing capacity for 209 calculating size of 46 designing 47 painting 187-9 materials 188 types of 188 use of gloss: on metal 189 on woodwork 188-9 panelled doors 133, 135 bottom rail 133 parts of 133 panels 133 paraffin: storage of 2 parapet roof 108, 229 copings on 109 pargetting: see rendering: in fireplaces partition walls 70-4 pebbledash render 187 percolation test 156-7 perspectives 5 petrol: storage of 2 use of 2 piers 229 attached to wall 58 block 85 brick 85, 209 compression loading on 218 construction of 56, 58 digging pits for 30 pad foundations for 44 setting out 26 pigments: paint 188 pile foundation 42, 45 short-bored 45 piles: bored 45 digging holes for 30, 33, 37 displacement 45 driven 45 short-bored 33 measurements for 45 timber displacement 45 pink primer 188 pipes, drainage: depth in ground 149 falls 148-9 flexible 152 joints 149-50 for uPVC 159, 160 rigid 152 sizes 148 types of 149-50 pipes, water: copper 174-5 for hot water system 174-5 iron 175 joints: for copper pipes 174-5 mains water 168 overflow 168 primary circuit 171 service 168 pitch: of roof 94, 95, 230 pitch fibre drain pipes 149, 150 pitched roofs 93, 95-106 parts of 95 structure 95 timber 98 types of 95 ventilation 112 pith: of tree 211 planing: timber 214 planners 7-8 planning approval 13 plans 13, 14 foundations 14 house floor plans 13, 14 roof 14 site 14 plaster: painting 189 plasterboards 74 for ceilings 185, 186, 187 plastering 183-7 applying 184-5 ceilings 185 materials 183 preparing surfaces 183—4 skim coat 187 tools for 184 plastic (PVC) drain pipes 149, 164 plate vibrator 82 plumb line 56 plywood 85, 88 gussets 101 pneumatic drill 36, 37 point loads 219, 221 poker vibrator 90 polings 35 polypropylene sleeves 150 polythene sheets: for roofs 101 preserving timber: pressure impregnation 214 steeping (immersion) 214 primer paints 188 privacy: with doors 129 profiles 230 locating 25 making and using 25-6 moving 27 protective clothing: wearing 1, 2, 3 public buildings 8 public sewer 147 pump: electric, for water in excavations 37 purlin 94, 230 roof 95, 106 with struts 97 trussed 98 putlogs, for scaffolding 115, 117 spacing ratios 117 structure of 115 PVC: pipes 149, 164 tiles, on floors 193, 194 quantity surveyor 6, 16 quarry tiles: on floors 193, 194, 195 quoin 230 racking back 52 radius: of arch 63 raft foundation 42, 43, 81, 83-4, 230 dimensions 83 rafter 94, 97, 220, 230 trussed rafter roof 95, 99 rainwater: disposal 162-7 outlet, on roof 111 pipes 163-4 dimensions 164 rammer 82 reactions 220 measuring 221 rebate 230 door 130 recessed mortar joint 52 regulators 5 reinforcement: in concrete first floors 88-90 cover 204 steel mesh, in floors 83, 84, 204 reinforcing bars: and compression loading 218 in concrete 204, 205 cross, for concrete stairs 127 for foundations 34 for lintels 59 for upper floors 89-90 rendering 230 in fireplaces 77 see also external v rendering; plastering retaining walls 34 reveal pins: for scaffolding 115 ridge: of roof 94, 102 Index ridge tile 94, 103, 105 half-round 104 right angles: making 23-4 ring main system 180 rise: of arch 63 riser, stair 119, 123 dimensions 122 road access: for site 12 temporary 18 rock: drilling 37 foundations in 34 igneous 66 metamorphic 66 sedimentary 66 roofs 92-114 coverings 93, 95, 101-6 functions of 92 insulating 113 parts of 93, 94 safety on 3 types of 93 ventilation 112 waterproof finishes 109-13 roof tie 220 see also flat roofs rubber boots: use of 1, 38 safety notices 4 safety skills 1 sand: for concrete 197-8 damp, water content of 201 silt test for 198 soil type 208 weight of 200 sanitary fittings 159, 161 pipework to 159 sapwood: of tree 211 sash window 139 glazed and hinged 139 solid battened timber 139 sawing: radial 213 slab 213 tangential 213 scaffolding 115-18 independent scaffold: structure of 116 inspection and maintenance 118 metal 116 connections 117 parts of 115-16 poles 116 putlog scaffold: structure of 115 regulations: for materials 116-17 for erection of 117 safety standards 2 timber 116 use of 115 screed 84, 185 board 184 bonded 190 cement and sand 190 granolithic 190-1 levelling 191 monolithic 190 vertical 186 seasoning timber 212 artificial 212 natural 212 sections 13, 14 security: doors 129 windows 140, 145 security fence: for construction site 18 septic tank 147, 153, 155 building 156 location 156 services: location, on site 12, 19 setting out building 23-9 columns and piers 26-7 corners of 24 settlement 39 sewage 147 sewer, disposal works 147 see also drains shear stress 218, 230 sheet roofing: on pitched roof 105 shower 161 side-hung windows 139 sink 161 silt 208 site: clearing 19 cost of developing 9 entrance 18 facilities 20 investigations 9-12 levels 10, 27 preparation 18-22 setting up 18, 20 servicing 19 sloping 30 digging into 33-4 suitability of 9 surveying 9, 10-11 site agent 6 site datum 27 skewback: of arch 63 slenderness ratio 58 slip 195 slump: of concrete 198-9 test 203 soakaways 156, 162-3 size of 163 soffit 94, 230 softwood 210, 211 boards 85 soil: classification 207-8 cohesiveness 208 effect of load-bearing pressure on 4l load-bearing capacity 43, 45, 207 particle size 208 technology 207-9 237 types: for foundations 41, 208-9 on building sites 30, 45 water in 208 see also subsoil; topsoil soil (sewer): drainage 147 principles of 147-9 vent pipes 111, 147, 159, 161 solar power, for hot water 172 active system 173, 174 passive system 172, 173 sole plate 73 solid fuel boilers 172 sound insulation: with doors 129, 133 span: of arch 63 of roof 94, 95 specification 13, 14, 16 sample 16 spigot and socket drain pipe joints 150, 160, 230 split-ring connectors 98 spot levels 10, 12 spring point: of arch 63 springer: of arch 63 springing line: of arch 63 staircase: reinforced concrete 89-90, 120, 121 steel 120, 121 timber, 119, 120 stairs 119-28 construction 120, 122, 124, 125 design 122, 123 dimensions, calculating 122 layout 121-2 length of, calculating 124 materials 119, 121 parts of 119, 120 types of 122-7 stair well 122 standards: for scaffolding 116 steel: anchors 62 staircases 120, 121 steps: tapered, on stairs 122 stepped foundations 30 strip 42, 44 stile: door 130 closing 130 hanging 130 meeting 130 and mullion joint 143 window 139, 143 stone masonry: tools for 66 stone, natural: for external walls 49, 50 building with 68 stone staircases 121 stone walls 65-8 building 66 coursed random rubble 66, 67 regular coursed rubble 67, 68 squared rubble 66, 67, 68 uncoursed random rubble 66, 67 stop: door 130 stopcock 168, 170, 171 location 171 stresses 217 bending 218, 219 types of 218 stretcher bond 53, 55, 68 string: stair 119, 124, 230 strip foundations 30 calculations for 46 concrete 41, 42 deep 41 detail of 31 dimensions of 47 height of, as site datum level 27 trench for 31, 32 see also stepped foundations: strip structural engineer 5-6 struts 35, 97, 220, 230 herringbone 87-8 making 87-8 solid 88 stud partitions 73, 74 studs 73 subcontractors 6, 13 subfloor: concrete 190-5 preparation 190-1 subsoil 41, 230 drain and open joints 155 excavating 31, 32, 37 irrigation system 155, 157 sump 37 superimposed loads 39 surface water drainage 147, 166 survey drawing 9 surveying site 9, 10-11 surveyor 2, 6, 9 swan neck junction 164 switch meter 178 syphonage: induced 160 self 160 tamping: concrete 202 tank, water: cold 168 hot, parts of 174 technicians 7 training for 7 tender 6 estimate 13 tension 218 termites: clearing 21 terra zzo: on concrete subfloor 190, 191-2 thatch: for roofs 93 thermosyphon 172 thinners: paint 188 238 threshold: door 130 throat: of fireplaces 77 tie beam 6l, 220 tiles, for floors: concrete 193-5 PVC 193, 194 quarry 193, 194 on timber 195 tiles, for roofs 101-5 interlocking 93, 101, 102 laying 104-5 section of 104 laying 101-5 plain 93, 101 laying 102 with nibs 101 ridge 94 tiles, on walls 195-6 cutting 196 techniques 195-6 thick bed fixing 195 thin bed fixing 195 types of 195 tiling battens 101-2 calculating positions 102, 105 fixing 102 treating with preservative 102, 104 tilting fillet 102 timber: drying 212 finishes on 195 for flat roofs 107 flooring 85 floors, suspended 84-5 joints for 215, 216 making, from trees 213 moisture content 213 for pitched roof 95-101 preserving 213-14 seasoning 211, 212 sizes 213 staircases 119, 120 assembling 122, 124 underside 123 structural limits 84 structure 211 technology 210-16 types 210-11 upper floor construction 85-6 structure 86 Index window frames 141, 142, 143 water exclusion 143 timber cladding: for external walls 70 for internal walls 74 timber mould: for block making 70 timber partition walls 70, 71, 73-4 timber scaffolding 116 tipper truck 36, 37 toe boards: for scaffolding 116 tongue and groove: battens 131 boards 85 tools: correct use of 1 for site clearance 20-1 top-hung windows 139 topsoil: removal 30, 31, 37 trades foreman 6 tradespeople 6 trammel 27 transoms: for scaffolding 116, 117 spacing ratios 117 window 139, 143 trap, drainage 147, 157 bottle 160 purpose of 160 standard sizes 158 types of 160 ‘U’ trap 160 tread, stair 119, 123 trees: growth of 211 parts of 210 for timber 211 types of 210-11 trial holes 9, 21, 30, 35, 45 trimmer joist 87 trimming joist 87 trussed roof 95 notes on 98 purlin roof 99 rafter roof 95 prefabricated 97, 99 trusses: connecting 98-9, 100, 101 forces in 219, 220 tusk tenon 87 Tyrolean render 187 undercloak 104 undercoat 188, 230 underlay 195 uniformly distributed loads (UDL) 219, 220 upstand 111 urban building site 19 valley: of roof 94, 102, 105 see also gutter: valley vent 230 ventilation 230 for indoor drainage system 161 for roofs 112 ventilator: window 139 verge: on gable wall 102 of roof 94, 105, HI vertical levels: from site datum 27-8 vibrator 202 vitrified clay pipes 149 voltage 179 walings 35 wall plates 84, 85, 94, 97 wall ties 65, 230 walls 48-75 building materials: bricks 49 block 68-9 stone 65-8 cavity 65 characteristics of 49 types of 48-9 see also brick, building; external walls; internal walls warping: of timber 213 water: for concrete 197, 198 in excavations 30, 35, 37 in soil 208 water bar: door 130 water flow: control 170-1 water heater: consumer unit 178 wiring 180 water meter 168 water pipes: with timber partitions 74 water pressure 168 water supply 168-76 cold 168-71 community 169 domestic 170 hot 171-4 water table 35, 230 and foundations 39 water-thinned paints 188 wattage 179 WC (toilet) 161 weatherboard: door 130 weather-resistance doors 129 weather-struck mortar joint 52 wedges 35 weigh-batcher 200, 201 well: see stair well white spirit 188 wind loads: see load: wind wind pressure: on windows 138 window cills 139, 143-4 heights of 28 windows 138-46 bottom rail 139, 143 building regulations for 139 combination 140-1 dimensions 139-40 fixing 144-5 glazing 141-3 louvred 141 metal 143 parts of 138, 139 security 140, 145 top rail 139, 143 types of 139 wiring: circuit 177 electric 2 domestic appliances 179-81 with timber partitions 74 wood float 90 wood: mosaic floor 192 strip flooring 192, 193 see also timber working drawings 5, 13-14, 30 symbols on 14, 15 working platform, scaffold: regulations for 118 yokes 58 zinc chromate primer 188 THE TIVATE , SERIES Macmillan's Motivate series has been a highly successful and best-selling series for many years. It has been created in recognition of the need for practical, appropriate and up-to-date technical and vocational core textbooks. Each textbook provides valuable instruction for students and home-learners undertaking the various technical and vocational courses and programmes in secondary and technical schools, colleges and other institutions of education and training. The series is constructed around the principle that each title must be relevant to the reader's needs and must provide a fully comprehensive study and understanding of the subject area. Each title in the series will be of use and interest to students and teachers alike, whether already practising their subject, or studying it for the first time. Teachers and lecturers will find that the texts contain all they need for presenting their subjects fully and effectively. Each text in the series has these key features: A wealth of information, providing both theory and practice of the subject material contained in course and syllabus requirements. A modern layout and graded language for improved readability and understanding Highlighted key concepts, ideas, safety points and areas of knowledge Numerous illustrations, examples and exercises A clear and full introduction and explanation of each topic, setting up a strong understanding of the subject and allowing quick progression of knowledge End-of-chapter summaries allowing for self assessment and revision, followed by exercises and questions Full answers to the questions, along with answering hints A comprehensive list of key words with concise definitions for revision Each text in this series has been written by experts in their particular field with years of experience in teaching and presenting the subject. Building Construction Principles and Practices fully meets the requirements of building and construction syllabuses in the technical and vocational curriculum of both senior secondary and college levels. The text provides practical information and theory on typical building techniques and materials for students who plan to work in the construction industry. Titles in the MOTIVATE series Building Construction: Principles and Practices Business Management Studies NEW EDITION Computer Studies and Information Technology NEW EDITION Electrical Installation: Principles and Practices Essential Mathematics for Technicians Introductory Radio and Television Electronics Metalwork Technology Motor Vehicle Technology for Mechanics Practical Electricity and Electronics Practical Plumbing Practical Welding Refrigeration and Air-conditioning Technology Technical Drawing with Design Textiles Woodwork Technology 978 0 333 60522-6 978 0 230 03039-8 978 1 4050 7450-6 978 0 333 60160-0 978 0 333 67796-4 978 0 333 61656-7 978 0 333 60054-2 978 0 333 60159-4 978 0 333 60056-6 978 0 333 61657-4 978 0 333 60957-6 978 0 333 60958-3 978 0 333 60161-7 978 0 333 61658-1 978 0 333 60053-5 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - BN 978 frica.com - 333 60522 iPptft

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